That's a common place for pressure for many good bowlers. I think some coaches even suggest strongly that the ball should rest in that area.
So I don't think there's anything wrong; it's just a place of pressure, where calluses build up easily. Where there are calluses, a blister will eventually show up. Put a pad or a band aid there, or maybe just a piece of tape.
To heal the blister, use aloe and/or vitamin E or a hand cream that has both in it and maybe a bit of neosporin covered with a band aid..
