HELP!! Can I be pregnant ?!

January 22nd was my second to last period! I had very unprotected sex on February 14th, and my last period was February 19th. 6 days before i was supposed to get my period which was March 12th, i had very light pink discharge the whole day. I was supposed to get my period on the 19. But I have not, so I’m 3 days late now. I’ve taken 3 pregnancy tests already. The first one came out slightly positive and the second and third negative... I’m so confused now.. i have some major headaches, low appetite and mild cramping, bloating and lower back pain. Could I be pregnant?