@cullin Apple will not repair your phone since it was water damaged. You can try and have an independent repairer like @refectio take a look at it. You need to let us know what Apple charged you for. Was it for a repair (doubtful) or an evaluation? I doubt you'll get a refund but you can always try.
This "I dropped it in water 2 months ago and it is starting to overheat, battery expanding, turns itself off, and dying even when charging." is a good sign of what is really going on with your phone. Most likely your battery has finally failed. You did not tell us if you ever took care of the water damage or if you left it untreated. If untreated then this would be about the time I'd expect corrosion to set in and your battery to fail. As much as I despise Apple and other companies that treat consumers like they do, this may actually not be their issue. Open it up, clean it, replace the battery and then re-evaluate.