I can't afford my car?

I purchased a used volkswagon passat 2006 about 6 months ago. Since that time I've had considerable expenses regarding health and home repairs. At the time I purchased the car the salesman told me I would not have a car payment for at least another month. My first payment was due before they could even finish detailing the car for me! (like within 10 days of purchase) I have been a slow payer from day one, because I just did not have the funds to make a car payment that soon after the purchase. This car payment and the insurance (collision/liablity) is killing me. What should I do to keep from ruining my credit?