can I still be pregnant??

Denise
So I had followed the smep this cycle and I got a positive opk 6th may, so we BD'd as the plan advised, 15dpo BFN, I'm now 18DPO and still negative and no sign of AF. My cycles aren't regulated they range from 28-36 days, am I still in with a chance or am I looking at another cycle trying?? Anyone has this before