Whats going on?

So, AF is 3 days late. I took a test the first day I was late and I got a very faint positive but then took a test later that night and they next day and they came out as a BFN. I don't know what's going on. My periods have been very regular lately up until this month. Someone please tell me what's going on. Ive been trying to conceive for half a year now.