What could be wrong with my Subaru?

If the oil is milky it has water in it. You may have a blowen gasket in the head, you need to have it check by a Top Nocky Mechanic, it will lead to a blowen engine or the engine siezing up. Get it checked NOW, Today do not wait!!!

Check your coolant too - my guess is that your head gasket is shot.

When it does not leak, it burns the oil. I am guessing you are a short trip driver doing most of your driving in the neighborhood or in town. Hardly ever doing highway jaunts of 50 miles(out & back=100m) at highway speeds of 50MPH+ so the engine never really gets hot for a long time.   The white stuff is condensation (water humidity in the air that collects up the tail pipe everytime the engine is shut off.)  This happens with every engine.  You would have to be in the middle of a desert where the humidity is 0 not to get humid air. [Most humans do not find that comfortable for BREATHING so they don't live there]  So, if you had been doing more longer drives then the moisture that is in the oil would have BOILED OUT AS STEAM.  The white stuff disappears.  

.   You NEVER wait for the oil change interval to check the oil.  Most truck drivers who have their own rig, check the oil level DAILY.(or the owner of the rigs have them checked each night).  Manufacturers are trying to sucker you into believing the car does not need checking of fluids regularly with a mileage reminder. 5000 miles or every 6 months. IF YOU ONLY DO HIGHWAY DRIVING THIS WOULD APPLY.  In town driving and short trips here to there it could take "Years" before the mileage minder light clicks on as to when the next oil change is suppose to happen.  

  "Oil is still cheaper than buying another truck." Chances are good the radiator is full of coolant. That would NOT be true if it was a blown head gasket.

. Many guys say "blown head gasket".  Yeah?  When my car is a VW Beetle with an "air cooled" engine, where does the water come from?  It makes them STFU and run away like little girls.   

Somebody does know more than them. (Like actual owners of vehicles.)  

You failed to mention the year of vehicle & how many miles on it.  It is very dirty, meaning carbon from burning gas is mixing with the oil.   It won't hurt anything.  My oil was Blacker right after an oil change, but I knew I was burning oil as that was soot colorant.

.Charcoal is like the soot in a chimney. It is greasy and black and soft.   So is a colorant called black. Kind of like crude oil when it comes out of the ground, it is black too.

.  I needed rings(bottom of engine rebuilt) and you also do the heads because the valves have the miles on them too.   I let it go and just added or changed oil & filter every 3000 miles with cheap oil(like WalMart)

.  When you have a minute try this experiment. Get a candle.   Light it.   Now pass your hand over the tip of the flame so the fingers go into the tip once.  Look at your hand.   Black soot.  You see none of it in the candle flame.  That is what gasoline does.  It burns with black smoke. Like a tire fire.  That is carbon smoke. Again like the chimney where you burn wood.

. Short trip driving is considered to be HARSH driving conditions. On the engine.

. If you have 100K miles on the car, then it is getting tired & worn out.  If it still runs real good, then just check the oil more often and change it more often, like every 3000 miles with REGULAR OIL.  Synthetic is money you are burning away. You will be fine until it sucks in a valve.  But you will know that happened when the engine clunks and stops running.

. Maybe you will have a good choice of EV's and maybe you live where the snow never leaves so an EV is useless.  Not a choice for you. Petrol vehicles will be around for quite a bit longer.

I look down farther and you say you change the oil filter and the tailpipe is the normal color.  What color is NORMAL TO YOU.   Mine was black and has always been black in  all 2 dozen different cars (except when I do a long highway drive, then the tailpipe went brown or grey white on the inside(meaning the engine is burning HOT.  When the tailpipe is cool, stick your finger up the pipe hole and rub off some of the inner wall onto your finger as you pull it out.  Now look at the finger. If it is black and sooty that is oil smoke.  No one has a chrome tail pipe on the inside for long - they all go black.  If finger is really sooty and greasy, yeah, oil smoke.  If it does not really come off the tail pipe and is black that is gas smoke. Which is more normal.  Finger can be washed off with soap and water.  Maybe by the time you wash the supper dishes by hand, they will be clean again.

35+ year mechanic.

It needs top-end work, either head gasket, or head gasket and cylinder head repair.

Older Subaru's tend to blow head gaskets which is indicated by the conditions you noted. Stop driving it as the oil is not going to protect the engine.

Are you changing your oil every 3,000 miles or every 5,000 miles if running synthetic oil? You also need to check the oil level every 1,000 miles between oil changes and keep it topped up. Don't go by any on board oil change reminder. They go too many miles between oil changes. If all the oil came out milky you may have a bad head gasket so go to a mechanic.

Subaru's are notorious for head gasket failures which can cause oil & coolant to mix, oil to be burned, and/or oil to leak.

Knowing the year, model, engine, and mileage would help determine if you have one of the engines that is prone to gasket failure and whether or not your car is at an age & mileage where its likely to become a problem.

In answer to questions regarding my question I did changed my oil filter as well as my air filter and my tailpipe looks normal in color. 

When you change oil, you should also change the filter.  Your question does not say you did.

If coolant mixes with the oil then it can cause millky oil but it doesn't look really milky to me. Maybe your car just burns the oil. Is your tailpipe black that is a sign.your car burns oil