HELP!

We've had a betta fish, Hector, for about three weeks now and he's not doing well. We have him in a 1 gallon aquarium with a whisper filter, a heater, and thermometer. There is a live plant and a small castle for him to hide in.

The first week we had him, though he wasn't eating much, he was very active in the tank. Then I came home one day last week and his fins looked singed on the ends. He was spending a lot of time floating on the top or laying on the bottom of the tank, either way leaning a little to one side. We went to the fish store and told them what was going on and they suggested changing the water and seeing how he did after that. Assuming we were talking to someone who knew what they were talking about, that's what we did.

Almost a week later, Hector still wasn't doing well. After much internet research, I diagnosed Hector with fin rot and went to the store and got Melafix. We changed his water (the medicine doesn't allow a change for 7 days) and gave him his first dose. He's had three doses as of now.

As of today, Hector's fins seem to be doing better. However, he's still not doing great. He is still spending his time floating on the top (still leaning to one side) or nose first into the bottom. His newest symptom is that if he does swim it is very spastic and jerky.

Does anyone know what is going on with Hector? PLEASE HELP!!