Hi moon lily!
I’m happy to hear that you and Bambam have a good relationship! Well first off, let’s talk about the vocal part; it could be seperation axioty, stress or abandonment issues. The mental health of a cat is a very fragile thing. It doesn’t take much to cause emotional damage. Seeing as he has had many homes—it could be the root of the problem. If so, you can only give him time and lots of love. A good trick to use if he cries a lot during the night is warm up some butter to a liquid form and put some on all 4 paws and tale. He will be busy all night clerning himself and too tired to keep you up. Another trick is a catnip sock; you put catnip inside a sock and tie a knot at the bottom and give it to him. He will bun out his energy trying to rip the sock apart and sleep most of the night. As per the vomiting, that’s not a good sign. Do you only give him wet food? Dry food? A combination of both? Do you know what he was eating before? Do you know if he was doing that before? If it’s been more than about 2 or 3 days I would suggest you take him to the vet. It could be a combination of things.
I hope this helps please keep us posted!