Popped blister not healing.?

Okay so one day I was on my scooter riding around town, and then I feel a sudden sharp pain on the bottom of my big toe. When I checked to see what was wrong, I discovered that it was a popped blister. It's about the size of the pointing finger's nail. It's been a week and it's looked the same, except the skin on top of the pop is yellow and hard compared to the rest of my skin. The blister is where the bottom of the big toe, like the other side, but where it bends. What should I do ?