Tricia,
Welcome to the forum. Sorry to.hear of the problems. The first thing you should do is contact the seller and explain whats going on with the fish. Its important to keep them in the loop. They may have suggestions for you.
It sounds like the fish may have a bacterial infection. Do you have another tank to use as a hospital tank? If not even a plastic tub or garbage can will do. You really dont want it shedding pathogens into the tank so it should be separated. You can try epsom salt (magnesium sulphate) from the drug store at 1 tablespoon per 10 gals that may flush out its gut. You will probably need to use an antibiotic.. maracyn 2 is a good choice and usually found at petshops...alternatively kanamycin sulfate can be used or furan 2 as a last option.
hth,
al