trumpet gets harder to play (trumpet acting weird)?

There are several things that I can think of.

First is the mouthpiece which is the most important thing, more important then the instrument. Perhaps there is a dent on the shank which can increase the resistance when playing. Does the instrument have dents on the lead pipe (where you stick the mouthpiece into) or on the tuning slide. Again, dents can mess around with playability.

Second, improper warming up and practising. When you warm up you should start on low notes like the open C (concert Bb). Slowly get the lips to vibrate and progress higher and lower. Long tones are good. You shouldn't be trying to play really high too fast because it will quickly wear out your lips making the higher range harder to play. Also, high range takes time to develop and playing it too soon will easily wears out your chops. You will be able to play your high G and beyond eventually as you practise. You also probably need to gain some endurance because your embouchure doesn't have a strong enough foundation yet. I am willing to say that it is mostly to do with how you are using your air.

Lastly, your instrument. Although YOU can clean it as many times as you like, there are some things that can only be done at the repair shop. An ultrasonic cleaning can help remove any gunk that still remains such as the hard to reach areas. The valve pads may need to be replaced because in time it compress and make the valves not as aligned.

Hope this helps.

it's like describing a problem you're having to a doctor via the internet.

it won't be a proper diagnosis given.

i don't play trumpet but just out of experience your best bet is to take it down to the music store & ask them, it could even be a scratch in it somewhere that has gone through, hence you need to blow more to get a sound out of it.

it could be anything to be honest.

check out Flea (RHCP bass player) he was considered an upcoming prodigy on trumpet until his friend Hillel (original guitarist) turned him into the maniac bass player he is now.

he still plays trumpet live & on some of their tracks, as for how good he is i can't tell you, it sounds good though.

Has anything changed about your practice routine - specifically are you warming up sufficiently. I know I had the same frustration because I wasn't patient enough to warm up properly. My horn (more likely my lips) won't cooperate otherwise.

For perspective remember what Dizzie said:

"Some days you get up and put the horn to your chops and it sounds pretty good and you win. Some days you try and nothing works and the horn wins. This goes on and on and then you die and the horn wins."

I don't know if this would work but did you check the tuning slide? Did you check the actual airway pipe things for obstructions? Is your mouthpiece alright (no dents, stuff like that?)