“Worried about pregnancy?”

I had sex with someone about 10 days ago. He used a condom, and didn't orgasm at all. I got a UTI afterward and was in a lot of pain from that. I took Nitrofurantoin for 5 days for that. I also got some cramping and lower back pain, that lasted about a week. I was supposed to get my period yesterday and never did. I'm really worried I could be pregnant, but I don't think it's really likely. I've been really anxious over this the last couple of days.

Except for lower back pain, a little bit of bloating and some cramping (which I'm telling myself is PMS; I was also experiencing this before we had sex), and some stomach pain (which I'm thinking is anxiety), I've been feeling fine. I started running 3 days a week 2 weeks ago, and have been tired as I moved 2 weeks ago. I started drinking a lot more water as well. I also went from living in a house of 5 girls to being the only fertile woman. I was on birth control until about November, and my cycle is usually about 21 days, give or take a couple. I took a pregnancy test a week after we had sex (even though I know it was probably too early to test), and it was negative. I'm still really worried I could be pregnant, and just wanted some medical clarification.