What Is The Cure For Dry, Itchy Skin At The Base Of Penis?

I've got dry ichy skin at the base of my penis, it goes through stages of redness which gets inchy and then it's fine and starts to dry up like it's going away, I'm not sure what this is, and just worried about it, I've been applying dry skin moisturiser cream to it for a couple weeks now but there has been no improvement, I have a girlfriend and we are sexual active and have sex or oral sex at least 3 times a week, but we are both clean of any STI's ect!
What do I do?