Period Late

Hello everyone! MY situation pretty much like most of you. I have had sex doing my ovulation window which was on the 1and2nd of this month and had sex the week after my window period. ME and my boyfriend has unprotected sex and I'm not on any birth control, we last had sex on the 13th his fluids came inside me, I was supposed to start my cycle period on the 15th this month I'm late.Feeling moody nausea and tired I'm also pushing him away, I took a pregnancy test at the Dr office on the 8th it was negative. Been thinking of going to buy a over the counter test. Any advice guidance maybe Thanks!.