UTI, Antibiotics, Pregnant? Can anyone relate??

So on the 29th I came down with a UTI. I tried to fight it off for a week or two and I started to feel better, and It came back so I went to the dr. And she gave me antibiotics. 
Can antibiotics delay your period?
When I was feeling better we had sex on the 6th. And we didn't use a condom. He never came in me, but now I'm worried because my period is a week late. 
I took black cohosh & vitamin c today and yesterday to see if that would help my cycle start, but all and today (I took the supplement this morning and didn't take anymore today) and now tonight I've gotten are massive cramps in my abdomen like I'm constipated. And the only thing that has helped relieve them is heat. 
I took a pregnancy test today and it was negative. 
Help! Why isn't my cycle starting and why am I cramping? I'm trying not to stress about this but I am, which is probably delaying my cycle even more.