cppietime

A few years ago I bought a banana(I think dwarf Cavendish). It was very young, grew to be about a foot tall, sent out a pup, the main plant died, and the pup continued growing. This happened about four times. Now all that's left is a small pup, about 3-4 inches tall that hasn't grown or really changed at all for about three years(sorry, no pictures at the moment). It's in an 8 inch-or-so pot.
Someone working at the nursery I bought it from years ago suggested I fertilize the plant more, as bananas are heavy feeders. I've tried this, and now the lowest leaf started wilting, and some of the other leaves have gotten edge burn.
Have I actually over-fertilized it now? How would I tell? What would I do to fix it? This is really irritating me.
Also, how do I know when to water it? I heard the "dry to a half an inch," but the pot is much bigger than the plant is now and the soil is pretty much always damn(I could easily go a few weeks without it seeing a drop of water and it would still be damp). Should I still wait until it's dry to half an inch, or should I go by some other means? Is it possible I was overwatering it? Underwatering? By the way, I live in New England, and the plant is grown in a heated sunroom next to a south-facing window.
Any and all advice is greatly appreciated, thank you.
EDIT: When I get a chance, I shall add the pictures.