Discharge while fingering?

So when my girlfriend fingers me or I do myself, at first it's a bunch of white discharge that's just in random bits and pieces. I find it SO disgusting and an insecure about it, but she doesn't care. She says it's not gross and promises me not to worry. But I still feel it is. Idk what's going on, bc it's not a yeast infection and I've tested negative for all STDs. Help!