weird discharge after sex?

I’m on birth control (Sprintec) and for the past month or so I’ve been regularly having sex and at first I would get a lot of discharge after having sex for like an hour or so, but it was always just my normal discharge. The past week or so, every time I have sex I get this weird light brown discharge that’s so thick it’s almost not liquid anymore? It’s a really weird consistency and it’s making me concerned because it’s an excessive amount, to the point where my whole underwear is covered within 20 min and it keeps going for up to 12 or so hours after? Does anyone know what this could be?? I did a bit of googling and a lot of websites point to birth control but said nothing about it occurring only after sex. I’m about two weeks from my period if that’s important.