What is it?

So I’ve been with my bf over a year (I’m 16 he’s 18) today we had just finished having sex and he was siting there naked. I was looking at his balls and realized on the left side of his ball there’s little lumps inside of it and I can see the shape of them on the outside. I’ve never seen this before. I asked him about it and he said he got it checked out along time ago and the doc said it was fine. Somethings weird about it though and the way he said it didn’t sound too convincing. What could it be??