Where to start...
I always wanted a big family. I thought three or four. But life got in the way. A lot of job insecurity and changes. A lot of moves. My first was not 'easy' - not well for the first year, but thankfully seems to have grown out of issues.
My head says its too late. We could afford another, but my job is a bit all over the place and my career would take a massive kick by having a maternity leave. I dont feel like I d have the energy.
But my heart cries out for another. Every time I see a baby, I physically ache to be pregnant again and bring another little person into our family. Everytime a friend announces a pregnancy or birth, while happy for them, I get really really upset (I hide it well though). Husband says our child is enough for him, but he will go ahead if it really means that much to me.
Our child is nearly five, so big age gap too.
So YABU - given age, career, age gap, unenthusiastic husband, etc, you are unreasonable to have another.
YANBU - follow your heart. You ll regret it bitterly in years to come if you dont. Husband wasnt amazingly enthusiastic about having first and now regularly says its the best thing that ever happened to him.