i took a dollar store test and it was a BFN today and im 2 days late is there a possibility im…

i took a dollar store test and it was a BFN today and im 2 days late is there a possibility im pregnant. i mean i have a 30 day cycle and i ovulated on the 6th this month but had sex on the 3rd and the 7th and on the 9th day 20 minuets after sex i wiped and had a string of blood along with his semen and the next day i wiped at 3:00 in the morning on the 10th and it was pink with my discharge? is this implantation bleeding? when can i take another test? i have an appointment tommorrow at the pregnancy center in my area and im afraid that will be a BFN too :( my boobs are really tender and im tired alot plus im bloating any input?