Miley,
He is going to have to get into a cycled and heated tank to help him. I know you have been spending your money trying to get him what he needs but he is getting sick because he needs to be in a good tank with a cycled filter and heat. It is going to be so hard for him to get better with no heat but you cannot heat a 1.5 gallon tank. Is there any way you could at least get a large bucket (new one) and a heater? Then you would still have to do the daily water changes but you could medicate him and keep him in the bucket or even one of those plastic Kritter Keepers. Here are some that would be big enough to heat.
http://www.thatpetplace.com/pet/prod...itemKey=204236 http://www.petsmart.com/global/produ...N=2030170&Ne=2 http://www.petco.com/Shop/petco_Prod...riums-_-center
Then if you can get a 25watt heater at the petstore, he will be set. Like I said if you cannot get the boxes above, a large brand new plastic bucket will do as long as you keep the water level down at least 2 inches from the top and white is the best color as it will make his world lighter and brighter.
He will eventually need a filter (sponge would be cheapest) but for the time being while you are giving him medication he does not need one.
He needs some Jungle Labs Fungus Clear Tank Buddies or some Maracyn2 for treating him.
Rose