It sounds like defensive strikes...which means he wants to be left alone. If you handle him "regularly", you could be causing a great deal of stress. Stress equals a compromised immune system. So, your husbandry may be "top notch" but so much handling could increase the risk of him getting sick. Also...what are the ambient temps where he's being handled so regularly? If they're significantly cooler than the ambient temps in his enclosure, the radical shifts in temperature happening so often could also up the risk level. Looking at those variables, it's not so surprising that he might come down with something.

I have also NEVER heard of using vics or eucalyptus oils and would not dream of doing so. Order some F10 and read up on using it as a nebulizer...basically, putting F10 in a humidifier and using that in (or very near) his enclosure. Keep ambient temps bumped by several degrees as well. See if that helps. And as suggested, in the meantime, track down a vet that you feel comfortable using if these methods don't clear things up. If the infection has progressed too far, you may need a culture and antibiotics to fight it off.

Good luck.