How do I go about this?

So I'm 25 weeks pregnant. My husband had a very promiscuous past before we met and shortly after I got pregnant, I noticed he had some red bumps, which looked like sores, on his penis. He went his family doctor and they told him it was just dry skin and gave him some cream. They didn't go away and he went back again with sores to be told once again that it was just dry skin. He also had a blood test checking for stds after that but they all came back negative. Because I'm pregnant, I'm concerned it's more than that and I want to take every precaution for my baby and don't want to put them at risk. How do I go about telling my doctor I want to take precautionary measures for something that hasn't been diagnosed? I've been tested for all forms of stds upon getting pregnant and everything was negative but I know things can lay dormant. Also, my husband's sister is an ob and delivery nurse at the hospital I'm delivering at and is close with my doctor. How do I make sure they don't tell her "we're giving her precautions for herpes" or, god forbid, they give me a c section because of this and then they tell her why..?