I was told that you could get a false positive OR negative if you tested before 12 days.
It's way too early. Hang in there.
The gas and bloating is probably because of the progesterone supplements (I felt the same way after my IVF). As for the negative test, 5 days is still very early, so don't worry too much about that. If you want to do another HPT, I would wait at least a couple more days first. Best of luck with everything!