I'm pretty sure she isn't. I suppose it's possible, but it doesn't seem likely.
At the moment, I think she *might* be coming into heat, which would be nice - in a way! - we can at least put the question to rest fully and get her neutered.
But no, at present it seems like she was gaining weight...
Neutering may help, though these aren't the type of behavor problems that are typical to see in unneutered cats, as far as I know.
It sounds to me a bit like he's bored and missing you - if he's feeling under the weather as well, that probably isn't helping his mood any.
I suggest making...
Realistically, January was three months ago - that's plenty of time for a problem to develop.
You mention him losing weight, and you sound like it is expected, so presumably this is do to some change in his diet? That could be causing problems.
I would definately take him to the vet and get...
This!
This takes time and that amount varies from cat to cat. In my experience, the more persistant cats take about a week to two weeks, so be prepared for a bit of a haul.
They will settle down eventually.
This is actually VERY common kitty behavior, and I'm honestly surprised you haven't come across it before. It is play behavior (even though it doesn't feel like it to us!) and some of them are really persistant.
You mention not being able to close them out of the room - I'm going to guess...
Introducing cats does take time (and patience!), and she may well have mixed feelings about the baby. Keep an eye on them, but try to let them work things out - he will only benefit from a substitute mom if she takes on the role (which will undoubtedly involve discipline!)
Read the introducing...