My Girlfriend Just Got Her Third Period This Month. She

My girlfriend just got her third period this month. She got it at the beginning of the month, but she was late. Then, she got it two weeks later. This was a few days after she took the plan b pill. She just got it for the third time today. She took the plan b pill last week. She says its not a normal period. Could she be pregnant? Or is it just something else?