Please help!! What could be wrong?

For the past week or so, I've sometimes been feeling this weird pain that starts in my stomach, below my belly button, and it goes down, and seems to shoot all the way down to my urethra. Last week, for a couple days, I had been peeing a lot so I figured it was maybe a UTI and would go away like they do when I get one. I figured that the pain was part of the UTI. However I am not peeing so much anymore, I am just going normally now but the pain still comes every now and then.

Yesterday and the day before, I had horrible, sharp stomach pains. Like someone was dragging a knife through my intestines. A little while after (both days) I did have a bowel movement. It wasn't really hard or really runny. Fairly normal.

This morning around 7am I woke up with HORRIBLE back pain. So bad I could not go back to sleep. My stomach was in a bit of pain too, along with feeling a tad nauseous. I got out of bed and took a hot bath, and that seemed to help. After a little while, I got out. I put a towel around myself and then the nausea hit me again. I sat down by the toilette and I kind of dry heaved a few times but nothing came up. I felt a bit better so I got dressed then just layed around most of the day, slept a bit and haven't eaten much. My back has been hurting still throughout the day but no where near as bad as this morning.

I am otherwise health.

I'm 17y/o female. 5'3" and about 90lbs. Please don't tell me I need to gain weight, I know that and I am trying to. I'm not anorexic.