What Causes Swollen Stomach After Taking Cerazette Pill?

My daughter was on Cerazette pil for 5 weeks only, she stopped it because she was bleeding on and off all the time, 2 days after stopping she had a proper period but she is left with a large solid swollen distended stomach and looks 26 weeks pregnant. She is not because she has had test and a blood test HCG both which was negative. How long will this very swollen stomache last for, it is really upsetting her because she looks very pregnant. She is not in any pain just mental pain, she is getting married in 18 weeks time!