should i test?

Nicole
I'm on cd 20 with creamy cm. I had positive opk on the 26th I tested a couple days ago and it was a startling white BFN. I did have on and off sharp cramping and twinges for a few days and even got more tired but I'm scared to test and it just be a BFN. I took femara on days 5-9 this month... I should be due for AF IN ABOUT 4 days!