Hi My 1 And Half Year Have Small Lump Types

hi my 1 and half year have small lump types behind his ears. both sides. I observed one when he is 3 months old.. doctor was not concerned . now i see 2 (these are hard.. looks like bone)behind left ear and 1 behind right ear (this is what kind of smooth.. like they get in neck. .).do i need to worry.my next doctor visit is 2 years. i have 3 more months to go.