Do i have to pay interest on medical bills?

Depending on the state, it is likely that you do. However, MOST providers are willing to negotiate a bill. Insurance companies often pay them "reasonable cost of services" based on an average in your region, so why can't you?

With bills such as x-rays, MRIs, etc., ask to pay half. Office visits, and other issues, ask for a 1/3 discount. Many places will deal with you. They price their services with this in mind.