I have had it for about 3 months, not open just feels like a blister but no blister present, thought origionally that I had burnt the roof of my mouth while eating but it has never went away. When I take my Flecainide it has a bitter taste and the area that is sore burns. The area is darker than other tissue on the roof of my mouth. Can Flecainide cause a sore on the roof of my mouth?