What Causes Itchy Dry Patch Of Skin Underneath The Lower Lip?

i have a really itchy dry patch of skin on and underneath my bottom lip...i've tried vaseline, moisturiser, vitamin E tablets etc. it started about a year and a half ago and nothing has got rid of it for longer than a week or two. i've been to the doctors about it and they just say it's dry skin, but it's very upsetting because it's itchy and the skin goes red sometimes with small yellow spots on which obviously doesn't look nice! it started around about the time i began taking microgynon... could that have anything to do with it? please help, i'm getting desperate!