I want to cry, but I can't

My life is just getting worse and worse. I'm in my first year of highschool and the pressure that's put on me is starting to be too much, even though the year has barely begun. I had 3 tests today, the first classes and I had mental breakdowns before, during and after each and every one of them. I think my body doesn't know how to cope with this, because something happened during the last test. I wasn't sure when it started or why, but I had a sharp pain under my right breast, it hurt if I breathed too deeply so I struggled with that during the whole test. I want to cry so bad right now, but I can't because I don't want my classmates and friends to think something is wrong with me, so I decided to look for an online platform to vent on instead. I'm currently locked in the bathroom just waiting to clam down...