OP, I think one thing to say is, if you decide to have children that means you are accepting a commitment that will be there quite regardless of how you feel.
It's like joining the army in that sense: you don't stop to ask yourself halfway through a battle if you feel fulfilled. Your job is to get through and help your comrades to get through.
And like a soldier, you have to keep your gear in good order. Which as a parent might mean, see a doctor if you suspect there is anything wrong with your MH or any other health issue that might make you a less effective force.
Some of us actually find that quite liberating: when you know you have a job to do, and one that will have to be done regardless, it can free you to some extent from that terrible burden of always needing to feel fulfilled, of always needing to experience some kind of inner glow. Inner glow ime doesn't happen every day.
A baby quite frankly doesn't care if mum or dad feel fulfilled; it will get nappy rash if you don't change the nappy and that's that. It will not develop emotionally and socially if you don't talk to it and smile at it and cuddle it, and that's that. Love, as they say, is a verb: it's not how it feels, it's what you do.
I am not saying you should take on this commitment. But I am saying, if you have taken it on, then you are stuck with it.
Looking back on 23 years of parenting, I remember fun times, of course I do. Lots of them. Times when I thought "Look at me, I'm really rocking this parenting lark". But equally times when I could just have run off to Australia, when nothing I did seemed right, when the only thing that seemed perfectly sure was that this was a shitty day and it was going to continue being shitty.
Looking back, it's not the glowing, rocking-it-all days that held the purpose. It's the days when everything was shit and we felt useless and we still kept going.