Plan b paranoid

Had sex with my boyfriend Sunday he told me Monday to take plan b because he didn't trust condoms and didn't know if one of the four broke. When we did it I had missed a whole month of birth control before and had started taking it again two days before we did it. I took plan b Monday when he told me to but I am over 175 and heard it didn't work if you were. After I took the plan b pill I got really bad cramps and have the same symptoms of a UTI. I'm really nervous about this but he think we will be fine...