Pregnant or STD

Recently i have been cheated on. I didn’t find out until after my bf had sex with another girl and then had sex with me within 8 hours. I don’t know if that was the only time he cheated while we were together. It’s been about a week now that I found out and now I’m suppose to be on my period but I’m 4 days late... this has never happened to me before I am not on birth control we didn’t use protection I think he just pulled out. I have never been more than 1 day late for my period my period are super regular. Could I be pregnant or do I have a STD?