My stomach is getting really big, whats wrong?

No, I'm not pregnant. Or at least I don't think I am. I haven't had in like two months, and I had my period. But like my stomach is getting really big, like to be honest I do look pregnant, but there's no possible way that it's why I'm getting big. And like my stomach constantly hurts, like not really bad but it's a constant little pain. And especially in the morning and at night it really hurts, like it makes me just want to take off these jeans and put some sweatpants on. And like on the bottom left side of my stomach, like above the pelvic bone it sometimes hurts. What could be wrong? It's been going on for the past 3-4 days.