It comes out in all different ways, some get blisters on hands, feet, around and in mouth and on bottom, others only on one area, sometimes they say they can have no blisters at all.
You really don't need the doctor unless your little one has persistent fevers with it (even then they won;t do much) - usually they say to let it run it's course. I think it's in the same family as slap cheek and several other viral infections, all which you can't treat with anything.