What Causes Abdominal Pain And Light Menstrual Period?

My girlfriend and I had intercourse on 18jan we used a condom but also to be on a safe side we used I pill within minutes. She was expecting her period on 23jan but on 25jan she had brown discharge followed by very light flow. It's 11 Feb now and she is experiencing abdominal pain since last few days. For few hours everyday. Is this some to worry about??