I agree with BNLs, new pdoc perhaps and new meds. If he's 18, there are some drugs that are okay for adults, which he now is, but not for children. Perhaps Lamictal or another mood stabilizer and/or an atypical antipsychotic (for racing thoughts/depression) or an antidepressant. Only a Dr can tell, but his monotherapy doesn't sound like it's working.

Sorry this is so tough right now.

Hope you can find someone who will help you and your son and have them not give up on him.