There's a lot of things here preventing you from getting a loan. Honesty is the best policy, so here ya go:
1. FOUR months isn't very long. Maybe not even long enough to be showing on your credit. Even if it is, four months of having just one credit card really isn't proving your ready for the responsibility of a car loan.
2. The mileage is killing you. Traditional banks don't like to do loans on cars with more than 60,000 miles MAX. They're just not likely to last the term of the loan, and who's going to pay on broke-down car? They can assume that in addition to the car payment your going to at least have some repair bills beyond oil changes.
3. $800/month? It's just not enough. Loosley speaking, you can get approved for 20% of your monthly income to go towards a car note. In this case that's $160. Banks are seeing that you need to pay for car insurance and gas on the vehicle, in addition to living expenses.
These things being said, this is a loan your FATHER is taking out, puting you on it to help build YOUR credit. If his is bad or if he already has a vehicle or two on his credit it's going to be tough. You're going to need second chance banks that dealerships have access to. These aren't your typical banks that do a multitude of things- you need a bank that just does car loans.