I od'd on adderall (dextroamphetamine and racemic amphetamine) a year ago. before this i was a visual thinker, now i can't do it, it hurts my abilities to think/learn. is this brain damage?

Possibly: Sadly, Adderal in large doses can do lots of serious damage - brain damage is among them. I don't know specifically about visual thinking modes - but overall cognitive loss and other problems can happen. It's a big price to pay for a mistake. I'm sorry it happened. But, you may still have what it takes to succeed. Some really high functioning folk, cut 50% are still above average. Hope and work!