Crampy low stomach and back for 3 days like i'm getting my period but i haven't got it . is this pregnancy ?

Could be: If you have been having unprotected intercourse and your period is late,you could be pregnant. To know for sure, do a pregnancy test and, if it is negative and your period still hasn't started,repeat it in 3-5 days. The lower abdominal and low back cramping could also be due to an UTI so it would be a good idea to get a urinalysis. Hope this helps.