SOMEONE PLEASE ANSWER MY QUESTION

My boyfriend and I regularly have sex. I've noticed this a few times, and I'm just confused. It doesn't happen everytime, but there's this substance, that I presume comes out of me. Now I know what you're thinking, this girl is so stupid, it's obviously cum. But it's not, I am 100% sure it's not. It gets on his penis, and normally is on the outside of me. It's sort of milky and very texturized. I guess its discharge, but I'm not sure. Has anyone else had this happen to them? I'm not worried, I'm just a little confused.