Dear CpaDave,
I offer an intimate personal reflection that you may find helpful.
My life plan at age 22 was to remain forever not only childfree but single. No responsibilities, plenty of time/money/energy to do whatever I felt like. I would be awash in sports cars and killer stereos and ski trips to Vail and Switzerland.
But in a very brief interval which passed in a blur and now is barely within memory, I married DW and the first of five children showed up. I was overwhelmed and confused; my plans gone with the wind.
Each successive birth fastened another shackle onto my failed ambition. By child #3 I grew desperate to find some distraction. I contemplated either entering grad school or taking a highly destructive action that I won't elaborate on. I chose school.
Immersing myself for five years in heavy learning worked. Thermodynamics and tensor calculus occupied so much brain that I didn't have time to think about my former plans. And then a miracle occurred...
...child #4 was born. Instead of inspiring apprehension, she brought light and love and more happiness than I had ever known. A few years later, child #5 did the same. I wouldn't trade them for all of Danmar's money.
The difference was in me, not in the children. My first 3 also were (still are) miracles, I just hadn't been ready to understand. Now I do.
***
We can't govern what comes into our heads, so it's best to accept that thoughts and feelings will enter unbidden. Helplessness, frustration, exhaustion, envy... all those will show up on our mental stage from time to time. That's normal.
It's also normal for them to pass. Won't happen overnight, so give it time.
But if merely unpleasant feelings like weariness give way to dangerous feelings like despair and depression, don't wait. Seek professional help beyond just the anonymous advice of a chat forum.
***
P.S. What if I had followed my original plan of luxurious bachelorhood? Knowing what I know now, I would undoubtedly have turned out to be a total prick, selfish beyond measure, surrounded by cold, empty possessions. Of course, I'd also be retired already, so maybe... Ha! Just kidding! Seriously, I'm better off the way it turned out.
Pax vobiscum.