Okay , So my period is about 21 days late and my boyfriend and I have been having unprotected sex ! I Went to the clinic and got a pregnancy test . They took my pee and my blood and both came out negative ! After we found out it was negative we had sex on three of my high fertile days and a day after ovulation ! I Been having stomach aches after I eat , Breast been hurting , Nauseous , Throwing up but not so much and Diarrhea ! Is there any other reason My period could be late ? And no I am not stressed out

It depends on how long you have been menstruating. If it hasn't been very long, your body will not be very regular. Sometimes it even takes years for your body to adjust. Personally, I have been getting periods for almost 6 years, and mine are still irregular. I Been Having It For About 7-8 Years and always haves it been on track sometimes a few days but never 21 days late