Welcome. Glad you are here and we are here to support you. Feel free to ask questions and I am glad you are less worried, but it still can be a lot to go through.
I have broad shoulders too and thought for years it was normal, I lifted and I too thought it was mostly pectorals (under some fat) as I lifted some and had muscle even though I always had a softer looking body and thought it was just extra weight. I don't know when it actually started but probably somewhere between 25 and 35 - I just wasn't tracking. It turned out in my mid 40s I started to realize I had gradually developed some breast tissue over the years. Now its clear that's the case for me and it's probably been aggrevated by meds I need now that 60 is in the future.
Congratulations on becoming a father, there's a lot of great stuff to look forward to. There's a lot written about how a lot of guys can physically change during their spouses's pregnancy, and I don't think it is well understood so that and your prior condition may be contributors, I am glad to read you got it checked out. You may have also read TRT can end up contributing to breast tissue, so its possible that may have been a catalyst as once started it can stay in motion even if very slowly. It could also remediate after your child is born.
Again best of luck and welcome. You'll be surprised how many people you can help because you share your questions or experiences.
Welcome and I'm glad you are here asking questions. There are no wrong questions and many answers to those asked. This isn't math with a single always correct answer.
I experienced the same health issues you have had and my noticeable change happened later in life. Looking back there were signs but not to bad. I have also had thyroid problems for 40 years which I feel is an underlying factor. Point is we are all different in body makeup, chemistry & environmental things to consider...
I was going to say what Midagemoobs2 add here. It's a real thing and little understood.
I was your age when I became a father. It was the best 20 years of my life. Ha still enjoying it as your always going to be the father they come to but its different. Make the best of it. Enjoy it. relish in the love parenthood brings and let this not become a large force in your life. If it is a problem and you see where it is causing health concerns delve into it and be your best advocate for answers. Many of us here just continue to live our best lives without problems.
cheers mate