HI jenn i'm jamie. I'm currently going through a problem with my leos that sounds very similer to yours.
First off STRICT and i mean STRICT quarintine nothing that comes in contact with this leo should come in contact with any other animal at all. Next step go to a vet with a fresh (no older than 24 hours). also bring the leo in to be seen and asked to have it's stomach flush so they can send the contents off to a lab to be tested for "crypto". Also in the stool have them check for any kinds of parasites but let them be aware you think it could be COCCIDIA. Coccidia has a direct life cycle and can cause death in leos. strick cage cleaning and quarintine should be used during medication. If it shows they have coccidia then albon will likely be the medication given.
You may want the ball pyton checked for coccidia if the leo comes up positive. Since coccidia can be transfered from contaminated water and fecal matter. Since the pet store didn't do cage cleanings. That really bothers me specially knowing there was a sick animal in the cage prior.
This is just a comprised post if you would like to know more on my situation and see if it compares to yours or you would like to know more about coccidia and how to disenfect your cages to kill coccida spores please go look in the tread "confused" in the leopard gecko forums. Or if you have any other questions i will be happy to help in anyway let me know either by posting, pm, or email. Please keep me updated on your leo.
Oh i know this is off subject but my sick leo phoenix ate on her own last night for the first time in over a month. And she is on albon cause she was diagnoised with coccida.
1.2 Bearded dragons (Login, Raven, & Jean Grey) 1.1.1 Corn snakes(Havoc,Sable, & Kink0 1.5 Leo's (Psyloke (Lucky-male) Speedball, Domino, Rouge, Siren, Elektra) 1.0 Veiled Chams (Neo), 0.1 Rose Hair T. (Night Crawler) 0.0.3 Crested Geckos (Shiva, Storm, Beast) 0.2 Kenyan Sand Boas (Tigra & Cloak)