Choosing ONE thing and seeing it through

What resources, tools, etc., would you suggest for someone who is having difficulty choosing just one thing and seeing it through? I go through phases where I have no clarity and cannot pick a goal or have any motivation. Then suddenly, I have great clarity on what i want. But as I start to work on it, I think, “well, no, I really need to work on this, too,” or “I have a handle on X (even though I have not come close to even achieving my goal), so now I will start working on Y, as well.” The end result is that I achieve neither (or, at best–I make minimal progress on one). An example would be that, I start off with the goal to lose weight, then want to add to it the goal to run a 10K, then a week or two later I want to also start working on all the things that are not perfect in my marriage, oh and shouldn’t I really come up with a plan on how to get us in a really great financial situation! This is a regular pattern in my life.

When I try to put this into a model, I don’t feel like I get much clarity (aside from knowing that I really, probably would be better off if I just stuck to ONE thing).
C–One goal, but then another goals comes to mind (I’m not sure if this is actually a circumstance?)
T–There is so much that I want to “fix” and I want to work on the other things too.
F–Eagerness to fix it.
A–I change and jump around between things.
R–Nothing actually gets done.

To top it off, even my one goal, is probably too big, to be manageable. For example, right now, I am 14 weeks pregnant (YAY!) and my goal is, when I have this baby, to be the healthiest I have ever been at the end of a pregnancy (I have other children). But when I think about what that means to me, it covers a lot: mental health (doing my thought work daily and restorative yoga/meditation), healthy eating (really focusing on managing my weight and eating healthy during this time), and physical activity (yoga, walking, swimming). And, literally, as I type this, my thought is “maybe I should actually work on communicating better with my partner and having less resentment.”

I’ve read “Essentialism” and I’ve listened to the podcasts on “constraint” in the past, but I can’t seem to get past the thought that all these are essential! I want to find a way to reframe some of this in my mind, because, in some ways, I’m not even open to a solution. I just keep recreating this pattern. Thanks for any support you can offer.