Severe abdominal pain...

Hello I'm 14 years old and weight about 45 kilos, I just woke up with really bad pain and cramps in my abdomen, then I got up and I started getting the worse abdominal pain and cramping, and it went right through to my back, and It made me nauseas and feel sick and hot. It keeps coming in waves, I'll be fine one minute and severe abdominal pain the next, it gets worse when I move around but it still hurts bad laying down. I have bad anxiety but I don't know if this has anything to do with it, how can I get rid of this and what is causing it, please help!

And I'm not sure if this could be causing it, but I was doing sit ups about an hour before I wet to bed