Okay i was scheduled to get my second shot between Sept 15-29 but didn't have time to go get on the 15th, I had unprotected sex on the 18th, three days later than my schedule can I be pregnant? I had been on my period and off almost threw out the 3 month since I got the shot and I have irregular periods before getting on the shot (would go monthes without having it) and I was on my period on the 18th the day I had unprotected sex but have been on it for more than a week... is there a big chance I'm pregnant