STD??

I had unprotected sex over a month ago. I took EX the same day. I had withdraw bleeding the next week. Then in June i had a 4 day period which is a little shorter than normal but I was bleeding enough to fill pads. Then a week after that for two days i’ve had brownish to bright red bleeding that only shows up when i wipe. it increases after I go #2. my bowel movements have been more like diarrhea today. all my pregnancy tests have been negative. I have some cramping as well. Do you think that it could be an STD causing the spotting?? i’m going to get it checked out soon, i just want some thoughts.