Geez, that cannot be good for any of you to wake up to screaming!!
Definitely check his food and make sure it's low in calcium & phosphorus.
The Cosequin should be helpful stuff.
Not sure as to the purpose of the Seacure? It's just a protein supplement? Doesn't he get enough protein in his regular food?
You might also limit his exercise to some calm walks for a bit, see if that helps things settle down.
Be sure you don't react to the screams in a way that might reinforce them... i.e. baby him, invite him to the bed, etc. Be calm and reassuring, but try to stay a little detached so he doesn't think screaming is a good way to get your attention or any other 'rewards'. I know I'm not thinking much if I get awoken in such a manner... mothering instincts kinda take over at that point for me.
Hope things calm down soon!