Help! what is this weird feeling in my stomach?!?!

okay so lately i've been getting this weird feeling in my stomach, mainly in my abs section. At first i thought i could've been pregnant but i've gotten my period three times in three months (normal cycle). I went to the doctor for my normal physical and blood test and everything is i good i'm health. But i have this weird feeling, it's like butterflies but not, and my stomach always feels really tight now, and if i slouch it feels kinda weird. I don't really notice if i'm not focusing on it. I've lost some weight (2-4 pounds) and i don't know if that has to do with it? i just don't know what's wrong with my stomach, anyone have any ideas? i just finished my period today too, so i don't know if it has to do with it? and also randomly yesterday my like left side of my armpit area started to hurt. helppp!