Hi OP - I'm going to try and say all this gently because I suspect you might be feeling pretty tired, stressed and emotional with such a young baby. If anything I write sounds harsh, I really don't mean it to.
The big thing that stuck out for me in your post is a sense of judging the dog for this behaviour. Phrases like 'wants to be centre of attention' often come with a judgement attached because, as humans, we can think people/dogs are selfish to want that. I think the first thing to call out is this is not an inherently BAD thing for the dog to want and I suspect is coming from a feeling in security and anxiety on the part of the dog. By all means, you need to address the behaviour, but if you can, it helps not to judge the dog for it.
The other thing that struck me is the relatively young age of your dog. I wonder how much interaction, focus, mental and physical stimulation he is getting now - especially compared to what he used to get. I could imagine having a newborn would mean there is little time to fuss, play with, walk and train the dog. And yet dogs need that. Some need it less, some need it more - but it is a fundamental need and not something they can just switch off.
Whining: you say you have tied everything but in 4 months you cannot have tried anything consistently because you just haven't had the time. I think the key is to remember that dogs do hat works. If he's whining then it is working for him in some way. For a dog desperate for validation (attention) even a telling off is a reward because you focus on him and interact with him for a few seconds. What you need to do is stop the whining working and instead, make effort to reward him for the right behaviour. If he lies down quietly (even for a second) then THAT is the time to focus on him and give him some fuss. You need to demonstrate clearly, with your actions, that whining dogs get nothing and calm, quiet dogs get plenty of fuss.
Guests: this is the same as whining and his anxiety will be what's making him worse right now. His strategy IS working for him and you need to control it so that it doesn't work. Things like instructing guest to totally blank him until he calms, and keeping him on a lead until then so he cannot upset them.
Behaving around the baby: he really needs to be shown how to behave. I think I would go about this by having two adults participate in the training. One to hold the baby (to make sure he is safe) and the other to focus on the dog - every time he is calm (even for a fraction of a second at first) he gets rewarded with fuss/treats. What you want is for him to IGNORE the baby - trying to encourage interaction between them right now is asking for trouble.
Finally, the dog has needs. He needs walking. He needs attention, fuss and training. I can totally imagine that being very difficult with a new baby (especially if you're not feeling great) but that doesn't change what he needs. Fulfilling those needs should go a long way to helping him cope.