What Causes A Missed Period With Weight Gain?

Well here it is..so at the end of august I had unprotected sex with my girlfriend and came in her. She took plan b about two days later. Her period happens around the beginning of the month and plan b screws with it. But she hadslight bleeding and was over soon. Then we had sex on the 17ish and I came a little early but not in her and was still hard and went back at it. She has not had her period since the slight bleeding at the beginning of september. Whhhhhats up? Oh and she went to the doctor and shes gained around 5 pounds.