Okay So Me & An Old Girl Friend Of Mines

Okay so Me & an old girl friend of mines decided we were going to have sex.. we started kissing and I got a little blood in my mouth but I thought I was just tasting the metal off of her braces. So we kept going and later on to find out she had a little cut in her mouth. But anyways I started fingering her (she was very wet) and then I decide to put the condom on and she gets on top of me..my penis didn't fit all the way only like the tip, I think I precummed a little but I DID have a CONDOM on but anyways like 3 days later I'm having like small stomach pains around the right lower stomach area... But I have also been taking Epsom salt baths for the past 2 days.. Do you think I'm just over worrying about it? The girl had sex with 2 other guys before me btw, & it doesn't hurt to pee or anything but I have been going poop a little more than usual. What are the chances of me having an std or sti?