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You should file a motion to hold him in contempt of court for failing to abide by the court's order. This can result in fines or even jail time.
As for him being medicated, I think this is nothing but a crock, and the judge should see through it. Unless he has documented evidence - a blood test or statement from his doctor - that he was under the influence of some drug when he signed the agreement, I don't think this is going to get anywhere. Also, he was represented by an attorney during the process and should have signed or not signed based on the advice of his attorney.
I think the judge will hold him in contempt and order him to pay you as he agreed.