I started playing again at the beginning of last month after a long layoff... (only played something like 4 hours between January and July). Obviously in the meantime my hands had softened up and this past month my tennis game has been held back by blister problems... These days there are only 2 that still give me trouble, but they're sort of weird: one of the side of the left index finger (for double handed backhands) and one right below my fourth finger on the right hand. They both look black, it seems some blood has coagulated beneath the skin. They're "flat", so it's not like a normal blister that breaks open after a while... Yet they hurt when I play or apply some pressure on them. What should I do about the whole thing?