What is the best supplement i can take to help build muscle and gain mass, i am taking keppra (levetiracetam) for epilepsy so it would need to be safe to take with it?

Keep it simple: This would be a great time to hit the gym really hard. You'll make friends when the people there see you are working hard. Resistance training will gain you the lean mass you want. Only if you do this will the creatine, protein powder and perhaps an electronic muscle stim unit (if ok with your dr) be effective. Especially with a handicap, this will be a wonderful gift to give yourself.