Is it possible I have dyslexia?

I do not think you have dyslexia. Dyslexia is seeing words backward. Like ekil. Anyway, you should see a doctor at least and eye exam. It could be from the concussion but you said it was happening before it so I would say you probably need to have your eyes checked. Not seeing well will cause your reading to be slower. If you are having problems in school, you can go to the guidance counselor and tell them what is going on. They will usually have tests at the school to check you out and see if you are needing some additional help. If it is found that you are having problems in reading and math and that it takes you longer at some things, there is a program in the schools that lets you have longer to take tests and to complete ignments without getting in trouble. Just mention it to the school, it could really help you out.