I'm going to remove the other threads and just keep this one since I think you'll get the most help in this section
My advice would be to stop medicating and get your water tested (at least test ammonia and nitri
te). Most pet stores will do this for free. It's hard to figure out what's going on without knowing your water parameters.
Four frogs in a 5-gallon is kind of crowded, I'd recommend at least a 10-gallon for that many frogs. It's possible that your current set-up is too over-stocked for the bacteria to keep up, leading to ammonia and/or nitrite spikes (both of which are toxic). I'm also kind of confused by your cleaning routine. Is the tank cycled? Regular full water changes (your monthly cleaning) might be stressing the frogs out (but it definitely wouldn't cause them to get that sick, they're hardy animals). What is your routine during these monthly cleanings?
What's the temperature in the tank, by the way?
If they were my frogs, I would set up a 10-gallon and use gravel from the old tank to kick start the cycle. If available, I would also use Tetra SafeStart (nothing else, even if a product claims to be the same). Then I'd move all the frogs to the new tank and monitor the water parameters closely.