I'm 20 days late for my period i'm cramping , having lower back pains i took a test wen i was 2 weeks late it sayed negative could i still be pregnant?

Maybe: Repeat the pregnancy test and if negative and still cramping see a gyn md to rule out pregnancy outside of the uterus(ectopic).

Not likely : Home pregnancy tests are very accurate and reliable. If your are two weeks late for your period then it should be correct. You can wait a few days and repeat it. If still negative then see your doc to discuss irregular periods and ovulation testing to help you get pregnant.