I Have Been Getting Tongue Sores Continuously Over The Last

I have been getting tongue sores continuously over the last two years, and occasional cold sores on my lip (I have had shingles 3 times, once during cancer radiation treatment). I have dry mouth, possibly due to Effexor medication, or some kind of after effects of breast cancer treatment. I also get itchy spots on my legs and shoulders, with scabs. Any idea whether dry mouth or medications are the causes, and what treatment might work?