Pregnancy or just a late period

Patient: My period is 3 days late. I’m on birth control and i’m supposed to be on my period today,(the water pills take 2 days to kick in) and i still haven’t bled yet. I’m sexually active,and my boyfriend has ejectulated in me a few weeks before i got on the water pills. but i was on my birth control the day he did anyway. Should i get a pregnancy test?

Symptoms: Nausea,back pain