Do I have a brain injury, I can barely speak in full sentences, come up with thoughts, ca?

This has been going on for months and I am really puzzled in the matter. Even when I try to come up with a thought, i lost it instantly, and I am told that it doesnt make sense, which results in slurred words. And its upsetting to me as I hear others having conversations and I cant process whatever is being said to me. For an 18 year old to be struggling with such cognitive problems (strictly speech, and comprehension, and not knowing what is going on), what would be the appropiate course of action.