Was the infection an abscess or from an injury? If it's injury related, then I would check with the vet about the relapse, as internal structures may not be healed enough, yet. Though too much confinement can slow the healing, and prolong lameness, so slow, easy exercise is usually better if possible than total confinement, for the sake of healing back to a functional anatomy, as well as avoiding the rip-roaring around your horse is doing the first chance he gets.
If it was an abscess, they can reoccur in the same place, especially if the vet or farrier probed it to drain it. The probing can introduce more germs and cause a quick recurrance as you may be experiencing. 9 times out of ten, I feel it's better to let it runs it's course with abscesses, rather than cut them to drain, because of the higher likelyhood of reinfection, and the fact that it's harder to keep the hoof clean after being artificially drained. If allowed to drain on its own *most* of them aren't a problem once they drain, but they can still boil back up, regardless. It usually depends on the reason that it was a problem in first place, if the situation that created the first one isn't remedied, then it can be a vicious cycle.
Recurring lameness in the same leg isnt' necessarily a death sentence, unless there is obvious trauma or this has been going on for months or years, but aquick phone call to the vet could calm your fears.