Cramps but no period help

I've been having cramps on and off for about a week. I just started birth control this month on the 10th. I had sex on the 26 of July, I took the plan b pill just in case. I got a light period 7 days later on the 1st. My doctor gave me a pregnancy test before I got the birth control that came out negative. Could this just be the hormones messin with my body?