Cramps and bfp

Br
Has anyone ever had cramps on the day Af was suppose to start and still got a bfp ??? I took a clear blue digital test and said not pregnant but I read some where that they take longer to show up Af is suppose to start today or the 17th glow had me set today because I was 29 day cycle last  month I'm usually 31 tho what do you guys think my chances are I'm say about a 10 percent chance sense I got a negative and cramps