L.-
I, too, want to have one more child. My situation is a little different. I found a swollen lymph node when our second child was 7 weeks old and was soon diagnosed with cancer. My oncologist says the chemo shouldn't affect my fertility, but having been diagnosed right after the birth of a child, I worry it had to do with the pregnancy and worry if it returns what life will be like for my husband having to raise children on his own.
Losing the weight is a very commendable goal. I wish you well and hope you are supported in your efforts. Everything I hear is that weight watchers is a great support plan (especially since they now offer it completely online) in addition to going to the gym.
I wouldn't be against going to a specialist if that helps (you're very lucky to have a supportive husband).
Like you, I feel I have room in my heart for another child. I hope we both get clarity soon.