I think we need more info on his screams. Does he scream in the morning, night before bedtime. Right before eating, if so, this is pretty normal for an Eclectus. If he he is screaming just to scream, then there is an issue that perhaps is not learned and perhaps a vet visit is needed.
It's true that at 10 weeks being weaned is super dooper fast for an Eclectus. If he regressed, this means he is not eating pellets, fruit, and veggies. If this is the case, then you may have to either spoon feed him or take him back to the Breeder.
There are so many reason that a Parrot screams, the faster you figure this out, the better off you will be. I agree that is not easy to listen to but I am thinking how this is effecting the Eclectus here. Can you describe his body positions when he screams, does he lower his body, flap his wings really fast, this is begging for parrots, perhaps there is something in the room that he wants or wants to be moved to another area. Is he close to a window, if so, move him, something outside maybe scaring him. Bird are pray animals and near windows are pretty scary for parrots.
He maybe screaming for your attn. Be careful here, don't always give in just because he screams.
I use the time outs with both my boys, This means, whenever my boys do something that is not wanted and after I have told them NO. I take them to their cage, cover them for no more then 5 min for a time out. Just like you would do with any child. After the 5 min and after they are quiet or calm down. I remove the cover, give them a treat for being so good and praise them.
Parrots respond to positive action more then negitive so kee0p this in mind.
Both my boys are very good, respond to me and thrive to make me happy. I live in a Condo and have never had one complaint. I hope this info helps. Best of luck Joe