Am I pregnant?

Good Morning everyone, I'm 22 years old and I been dating this guy for about 6 months. We been having unprotected sex for about 3 months now and I really think I'm pregnant because my period is 3 days late BUT I took 3 pregnancy test every morning and each one said negative. The first was from a doctor.  I never been late on my period and idk what to do at this point. Any advice?