My Horse Has A Sore Heel bulb?

I am not quite sure happened to my horse. I discovered on Friday he was limping slightly, I poulticed his foot and couldn't find an abscess. So yesterday I discovered just one side of the bulb of his heel is swollen & puffy. I wrapped his foot and packed it with poultice (on the heel), he's not limping anymore but it's still puffy/smelly & moist. If its not an abscess, my next thought it perhaps he nicked his heel with his back foot when we were trying out gaming. I was told one time that my horse steps in the same front footprint with the back foot. If this in fact just a nick, is the treatment i'm doing with the poultice not helping him or making it worse? If it were a cut with an infection, would I still want to keep it wrapped and in a boot? Please do say "call the vet" as an answer, the vet I will call, but first looking for opinions.