I think it's very interesting that your husband claims he always wanted to be a 'girl' but he didn't mention it to you until after you were married. This suggests that either he was lying to you then, or he's lying to you now.
I had a partner who decided he was trans after three years of us being together and him never mentioning it once. He was suddenly absolutely convinced that he had always been trans and that surgery would be the only answer to all his problems. I loved him so much and I was so worried about him that for a while all I did was consider his feelings. Eventually his demands became too much and I split up with him.
I mention this because after the split, he moved to a different city and saw a different psychiatrist. He then realised that he wasn't trans at all. He's spent the last two decades living happily as a man, and he recognises that his obsession with transitioning was a symptom of his poor mental health, not the cure for his problems.
I think the first step for your husband should be seeing a really good therapist - and not just someone who is simply going to 'affirm' him. If you can also have a frank talk to him about why he's feeling so dysphoric now then it might be helpful - but of course he may not admit the whole story. (For some men, it is a result of watching AGP porn for example). Ask him to show you all the websites, chatrooms etc that he's been looking at. His willingness to be completely honest about this will be revealing.
Please don't make the mistake I did and just put your husband's feelings first. You'll doubtless find that almost everyone around you will be rushing to put his feelings first too if he does choose to transition. Everything is set up to help the man transitioning and not his family.
Sadly I have seen that a lot of men who transition cite their fragile mental health as an excuse for unhealthy behaviour such as expecting their wives to keep secrets for them or trying things in bed that the wives are really uncomfortable with. Sometimes women carry the huge emotional burden of facing their lives being turned upside down all alone because their partners ask them to keep it secret. Meanwhile while the husbands are busy making loads of new friends (and some inappropriate friends) online.
Make a decision today to put yourself and your child first, and get as much real life support for yourself and your child as you can.
Best of luck in whatever you choose to do and I hope you find loads of support on here too.