16DPO and still getting BFN?

This is my second round of clomid, and by OPK test I ovulated around the 24th of April. Of course we BD'd a lot. I usually have a 28 day cycle, but I think due to the clomid I had a 30 day last month. So I calculated it to be 30 again this month which AF would of came today. I tested this morning with a cheapy internet HPT 25ml and it said BFN!! What are my chances of still getting a BFP or is AF just coming later than 30- days. Also when should I test again it gets expensive!!?