Hi, so my boyfriend and I had sex about a month ago and I haven’t started my period (but usually my periods are mess up like some time I have them at the end of the month or the beginning of the month like it comes when ever it wants.) well so I went to the store on Friday and got a pregnancy test because I thought I might have be pregnant, but it came back negative. I want to know if there is other reason for a period to be skipped? Thank you if you do help!