When you mentioned goosebumps the first thing that came to my mind was dropsy. I've never had any experience with it in any fish outside of bettas and goldfish, but I've supplied a link outlining the characteristics and treatment.

You mention double aeration...what type of filter set up do you have? Most of the time a healthy fish has a strong enough immune system to keep common aquarium diseases in check. How often are you doing water changes and have you had the water tested? While in most cases people say to buy your own test kit, if you aren't planning on expanding your tanks much further I'd say just take a water sample into any chain pet store. Unless they are your only option for buying fish I wouldn't recommend them for purchasing anything other than supplies or possibly plants, BUT most of the time they are willing to do a simple ammonia-nitrite-nitrate strip test for you. The PetCo near me even has staff that is fairly intelligent about the fish they supply...inquiring about your tank size and current inhabitants etc.

Good luck with your fish, and depending on your other fish in the tank and whether or not you have sensitive plants, definitely consider the salt treatment; mollies are known to thrive in brackish water.

Hope this helps!
Kayleigh

Here is a link that might be useful: dropsy

Sounds like your fish is has a severe and likely fatal case of fungus that has damaged its internal organs. You could try to medicate it in a quarantine tank. Don't medicate your new tank because you could destroy its newly built up bacteria population.