What Causes Sores On Fingers And Mouth?

I started getting sores on my fingers that were initially diagnosed as shingles but then I started getting them on more than my 4th and 5th digits as well as started to get them on my other hand. They come for a couple of weeks and then get a little better for a couple. The last couple of times i've started to get a sore in my mouth at the same time. I've seen a dermatologist and they said it was not shingles nor did they think it was any other derm problem and they sent me to a rheumatologist who seems just as stumped as everyone else.