I'm not a lawyer, but if I were you, I would contact an attorney immediately. Each state has a statute of limitations for each claim, which basically gives you a certain amount of time during which you can file a lawsuit. Since yours is a medical malpractice claim, you only have as much time as your state allows for that kind of claim. Once that time period expires, you may be out of luck (unless you discover a new harm from that incident at a later date).
The state you are in matters greatly in how long the medical malpractice statute of limitations lasts (past your 18th birthday). They range from 1 year in states like Kentucky, Louisiana and Tennessee to 6 years in states like Maine and North Dakota, but most states fall in the 2 or 3 years category. For this reason, it is important for you to talk to an attorney as soon as possible to make sure that you are still able to file a claim for medical practice, and to see if you have a possible case.