Always crying, anyone else relate???

So my son has always been a good sleeper he slept through the night, went to bed without fighting, and always slept a good amount. Recently anytime he’s put in his bed he cries and screams bloody murder until he’s picked up and then he’s fine but the moment he’s out bad he starts screaming/crying again. It will last HOURS. I haven’t been getting any sleep recently and I start school on Monday and we move into apartments on October 15 so I need to get him under control. Today he’s been crying at everything and hasn’t stopped. He has no fever, no teeth coming in, he’s fed, and he has clean diapers, he’s perfectly healthy. This is frustrating me to the breaking point. I also have a 2yr old who is also starting to copy his brother I am just lost at what to do.. it’s like one moment he’s perfectly fine and playing with his toys and the next it’s SCREAMING AND Crying at the top of his lungs. Again I check him and he’s fine. I took him to the doctor to see if something is wrong with him and nothing I’m just lost. Any recommendations??