So my 3 week old was sleeping great at night, about 4-5 hours at a time. And then all of a sudden he's been so clingy…

So my 3 week old was sleeping great at night, about 4-5 hours at a time. And then all of a sudden he's been so clingy and will only sleep if I'm holding him. I try to wait until I know he's out to put him in his bassinet but as soon as he touches the mattress it's nonstop screaming until my so or I pick him up. Any ideas on what to do would be significantly helpful.