To sum up, I have been in a faithful relationship with my gf for almost 3 years now, we have both been std/sti tested across the board since getting together trying to solve this issue with negative results across the board. 

She has rather large labia, which do seem to make it a bit more difficult to always keep lubricated (maybe that's a factor?) 

We've tried everything. Washing before and after sex (mostly helped but would still happen regularly as opposed to almost every session), only getting intimate in the shower, using lube, and it still persists. Once in a while the cracking will be followed with dryness around the open cracks and even more occasionally what look almost like tiny whiteheads on the head. All symptoms always clear within about a week, but persist on coming back whenever we try. It's starting to really hurt our relationship and just want to find a solution so we can get on with our sex life and just life in general.

 

What can I do to prevent this and why could it be happening?!