4 days late. BFN.

Been getting really bad pelvic pain & cramping but im now on cycle day 38 and iv never been this late. I keep doing tests but BFN. What cycle day shall I give it too before I book a gp appointment? It's really stressing me out im so upset because I just wanna be pregnant or come on my period. Its so horrible not knowing. Has anyone been late on period and got a BFN after late af and then turned out to be pregnant? I'm so confused :(