Hi, me n my gf had sex ever month or after 2 months later when we get opportunity. She always delay her period for about 2-3 dyas. We do protected sex and we did last on Dec end or starting of jan n her last date of period was on 21 dec thn after tht she were expecting her period on 21 jan but it doesn't work for her, finally it happens on 30th jan (9-10 days delay) and she feel pain enough at night. Why it is happening? Does it happening due to sex? Or something Else. She is not pregnant, we do safe sex Everytime.. plz answer me