Unfortunately, I don't have any ideas for treatments that don't require a trip to the vet. If it really is an abscess it will take a long time to heal and probably won't get better without veterinary treatment. In my experience, rabbits with abscesses don't do well and any antibiotics that you can get OTC are going to be far too weak to have any effect. Most commonly, the rabbits I've seen that have been able to recover from an abscess, particularly an oral abscess, have had to undergo surgery to clean out as much of the infection as possible and have slow-release antibiotic beads implanted at the site of the abscess. I just wanted to tell you not to stress your rabbit trying to look at teeth that you have no real chance of seeing without special equipment.
The other thing that comes to mind with the description of the weepy eye is a blocked nasolacrimal duct. That's the tear duct in the medial corner of the eye. If the lump is closer to the eye than the nose, that could be it. Usually my vet treats those with manual flushing of the duct (I don't know that you would be able to get the equipment to do that at home, plus it involves numbing the eye so that it doesn't hurt) and antibiotic eye ointment. But usually blocked ducts just display excessive eye drainage, I've never seen one that had a quarter size lump associated with the blockage.
