I agree, you may get better luck on the "Allergy" or some "Skin" Community. Try putting you subject into the search field, on the upper right of this page.
On the size of a dollar coin : ) Well I haven't seen one of those in circulation for about 60 years, so most here have no idea how big that is. Maybe you should say about 1.5" in diameter, if that sounds right. Heck, nobody under 55 even knows what a 50Cent piece looks like, or they may think a dollar coin is the the "Susan Anthony" (was that the name?) dollar which is about the size of the old 50 Cent piece. Sorry for the ramble, but reminiscing keeps surfacing in my agin mind
My experience with my Primary Care and an annual physical would be for such a complaint would be:: "go see a dermatologist". Heck, it might be time to get a general check up there too. All my recent "spots" are age spots, or at least no malignant - I have them removed on my face, that that may be a losing battle.
I think you are on the wrong forum. We are all the folks with the crazy heart rhythms. I'm sure there is a forum on this site that can give you some answers though.