Pregnant? Stress?

Me & my boyfriend had unprotected sex on June 6th while I was on my period (last day). He came inside me. I ended up taking a Plan B pill the morning after. My period didn’t go away until June 10th so it last 4 extra days. This month I was suppose to get my period on the 5th & it’s been 6 days & I still have not gotten my period. I took a pregnancy test 2 days after my missed period & it came out negative. (I have been stressing out a lot as well & my cousin tells me that I should be fine & it’s most likely delayed due to my stress, but idk) Could I be pregnant? Should I be worried?