I Have Tooken Plan B Twice Within Two Months Both

I have tooken plan b twice within two months both maybe 20 minutes after having the sex. The last time i took it a week later i bled so but it wasnt my normal bleeding it was a lot only 3-4 days and lighter then i usually do. But a few days acter the bleeding i got sore breatss and lower pelvic kind of pain and lower back pain almost like i have period symptoms again and im really scared. I dont know if taking plan b twice with in two months caused this or i should be worried about pregnacy? Please help.