White weird discharge with sex

So every single time me and my boyfriend have sex I have this white looking discharge that almost balls up, it almost looks like dead skin but white, and you can ball it up matter fact, it balls up itself! I’ve been to my gynecologist multiple times over this because it’s kind of embarrassing, I’ve been tested for yeast, bv, and all STIS, including all of the more dormant stuff like your Ureaplasma’s, and every single test is negative. I’ve also had a diagnostic PCR swab for all bacteria that could possibly grow in your vagina and everything is also normal and negative. My gynecologist says the only thing that she can think of is the lube that I use doesn’t go well with the pH of my vagina, but I use Joe water-based lube, which seems to be the best one from everything I’ve heard from other people! I wouldn’t be as embarrassed about it if it just was kind of like a white creamy substance, but when I say it literally looks like dead skin and it rolls up into balls in my butt crack it just kind of embarrasses me. He hasn’t said anything about it, but I know he notices it because he wipes it off after sex which obviously is fine, but has anyone had this issue and if so, does anyone know what it could be?