I have had what sounds like the same thing too for several years - at first I thought I was just very unlucky and getting mosquito bites on top of my moles/freckles which is silly
It's an annoyance but hasn't given me any cause for concern personally. I'm not sure what the cause is but my (uneducated) guess is that it's perhaps where the skin on top of a bumpy mole goes through its process of shedding, it can cause a slight irritation. The itch feels a bit like a histamine reaction, so it could also perhaps be something to do with an over-enthusiastic immune system.
I really don't know - just wanted to share that I have the same and it hasn't caused me any problems or become worse.