After 20 years, a fungus or
yeast infection seems most unlikely. Some people just lick their
lips constantly. The more you think about your lips, the more you can't help licking them. Perhaps a topical steroid might hep--they work better than Elidel, in my experience and mild ones are quite safe, certainly enough to be worth a try for a couple of weeks. You should talk to your doctor about that. But after all this time, you may just have to love with it, as you have been doing.
Best.