I don't know what to think...advice welcome

This is what is going on and it's driving me mad! Any advice would be great. I ovulated on cd25. Decided to take a test on cd38 and got what I thought was a very faint positive. I waited till the following morning and took another and it was negative! Waited a few more days until today incase it was the different brand of test but still negative! I'm on cd41 and af is nowhere to be seen. My longest cycle has been 37 since TTC. I feel so tired and I've got a really tight stomach and need to wee loads. I don't know what is going on. I don't want to give up yet!