What could i have ?

My body feels a little different sometimes i feel like im getting stabbed in the stomach the pain doesnt stay it comes and goes. Now i read sometimes if you have an std you dont get symptoms i dont feel any pain when i push down on my stomach down close to my vagina or near my belly button. I also have a weird smell like fish after sex i had sex with my boyfriend 2 week ago and i didnt have this smell i had sex with him 5 days ago and i smelled a fish smell and i was so embarrassed he is my new partner. Also the last time i had sex with my ex was about almost 2 months ago we still talk cause we have a baby together i asked if he felt a little different or if it hurts when he pees he says no he feels normal now my new boyfriend says he can never take a shit now is that a sign of an std ? I want to make sure what it is before i get checked out.