Mood Stabilizer for 5 Year Old?

Our five year old ds has been diagnosed with ADHD and FASD. He is super intelligent and sweet. No hitting or aggression. But we have tried 5 different ADHD meds, and they only help a tiny bit, but have other really bad side effects. My ds is also hypoglycemic, so not eating is dangerous for him. My issue is that I feel more that he's bipolar. His moods switch from manic (laughing non-stop, so hyperactive) to angry (yelling at us, rages that go on and on...) and right back to manic. He cannot be told no or have anything taken away. He will go ballistic. He was kicked off the school bus, and he hid under the seat screaming at the principal and kicking him, because he didn't want to get off the bus. He is majorly oppositional defiant, half the time. He will argue to no end. He does not want to go anywhere. His pre-k teachers say he's great, until he "switches". I really want to try a mild mood stabilizer, as opposed to an ADHD med, but I don't know if there is such a thing for a 5 year old. Is he too young? His mood swings are so far out of the ordinary that my dh and I are scared for him, and us. During one rage, he held a knife and looked at me like he was going to stab me. On the other hand, he doesn't typically hurt people or animals and is not fascinated with gore (he is fascinated with knives and guns, though...and looked at me when we were carving a pumpkin, stabbed the pumpkin with those kid carving things and said "Mommy, this is how you stab someone." How did he know???!!! Anyway, just looking for anyone who has had their child on a mood stabilizer and any suggestions.