Tightness in stomach sides

Okay I need help so for the past two days I been experiencing tightness or soreness on my stomach (like as if excerised and the next day felt the soreness). Idk what it means or it can mean nothing at all. It can be from losing weight because I haven't been eating fast food in like a week or so because I'm in the process of moving and only eating a little a day(not because I can't a afford food)but because I don't crave it anymore. and my period is late also.