I'm afraid it's time to go back to the vet. It sounds like whatever the wound was to begin with, it's now at least infected, if not a draining tract from a penetrating foreign body (like a foxtail). The swelling and oozing are signs of infection, and some antibiotics are probably in order for this to heal quickly and properly. If the vet feels that there is a foreign body inside the wound, they may want to sedate your dog and explore it to remove any foreign material causing irritation and infection.
This time of year, foxtails get everywhere, and they can cause some really difficult problems. The little barbs on the ends get embedded in tissue, and they just work their way farther and farther in over time. Ears, eyes and between toes are probably the places I see them most, but noses are right up there, too. Until they're removed, they just continue to be a source of chronic irritation and infection.
It's also possible your dog scratched himself with a toenail trying to get the foxtails out, and that wound is now infected. Either way, your vet should be able to help you get this resolved.
Good luck!