RI's usually come down to husbandry - your temps sound ok, so 2nd thought is ventilation, how well ventilated is the enclosure? its a difficult balance, ventilation vs humidity, but its important
I would suggest a visit to the vet, and ask them to take a culture to find out what the RI is (rather than just dosing up on antibiotics, the usual first response), given that your temps are ok, it could be a fungal infection rather than bacterial, so its important to know which it is
if it is a fungal infection, then it could be that the substrate and enclosure hasn't been ventilated enough, and has been overwhelmed with spors
what kind of substrate is it?
Bioactive is by far the best solution for humidity loving species, it helps maintain humidity levels and at the same time provides an ecosystem which can help prevent the buildup of moulds and fungal spors which cause RI's