Suggest Remedy For Irregular Periods

Hi..My friend is worried about her period, but she is too afraid to speak to a doctor so I told her I would help her out. She is sixteen and she is sexually active. Her period came four days late and on the first day it was heavy, but the second day was lighter and seemed to have dark red clumps, and was red, but it was also pink at some points of the day. Also she said her period usually lasts from six to seven days, and on day two it seems like it is ending. What could be the problem?