What Causes Late Period With Inconstant Pregnancy Test?

Last august I had my period on the 29 before that I had unprotected sex my period is irregular. The next month I got my period for one day and after 3 weeks got my 3 days period I'm sexually active for the past 3 months. Took a pregnancy test came out negative then positive then negative again. I'm suppose to get my period This week but hasn't come yet could I be pregnant. Is it just a false positive?!