sex with my ex

so a month ago i spent the night at my Exs house with his sister. around 1 am he sent me a snapchat and somehow lead to the conversation of his asking me if i wanted to have sex. i was a virgin at the time but i still went along with it knowing he had a girlfriend. i know it was wrong but i just missed having him to myself. he didn't use a condom and i wasn't in birth control at the time. two days after we had sex i got the shot and now i'm having cramps and yellow discharge. is that normal? any ideas on what i should do now?