There are three major low-cost, government-sponsored medical insurance programs that might be available for you: Medicare, Medicaid, and Medicare prescription drug coverage.
First, you can get full Medicare Part A (hospital) and Medicare Part B (medical) coverage, regardless of your age, once you've received Social Security or Railroad Retirement disability benefits for 24 months. Medicare sets out this rule on its web site page and explains how to enroll.
Also, if you have little income other than your disability benefits, and you don't have much savings or other assets (besides your car and the home you live in), you may also be eligible for Medicaid health care benefits. Medicaid covers most of the costs that Medicare does not pay, and pays for some health care services that Medicare doesn't cover at all. To find out about Medicaid eligibility in your state, contact your local county social services or social welfare office.
You may also be eligible for free prescription drug insurance under Medicare Part D. If you qualify for its low-income subsidy, you'll pay a small or no monthly fee to join a plan, and only a very small co-payment to fill prescriptions.