If anyone has similar experience with leaving a field (and somehow, a "project" that has been the center of one's life or dreams), I am happy to exchange about it.
I made a similar transition, but in the other direction. I left a doctoral program in a STEM field to go, ultimately, into my current branch of psychology, which I have found, on the whole, to be personally quite satisfying. My training program in this field was also the first time in my formal education that I was not young for grade, and thus automatically perceived as the young prodigy of the group, which was also an instructive and personally-enriching experience in its way.
I will say what I usually do to people of any age questioning whether they should embark on something new because of the time already invested or the time to be invested: in three years (or five or ten...), if you don't make this change, you'll be in the same place you are in right now...but the three (or...) years will have passed all the same. If you make a change, at least you will have taken some action to change your own trajectory.
Please do, though, take some time to reflect on the moments, thoughts, activities, circumstances, people, etc. that bring you joy, give you a sense of fulfillment and purpose, and help you to feel the most authentically yourself. I encourage you to look for patterns in those moments, and try to assemble a picture of the elements (personal, educational, career, etc.) that would contribute the most to a healthy, compassionate, and purposeful life for you. Keep in mind, too, that there are many different subfields within psychology and related domains. Retuning your focus may not mean discarding all of the credits you've accumulated.
On a different note, as to procrastination: I have a lot of personal experience with this, too.
For myself, I've found it helpful to be honest about the conditions under which I work best, and create systems for accountability that maintain those conditions when I need them. For instance, I work rather well to deadlines, but know not to allow work to pile up to the point that it feels overwhelming, so I've positioned myself in a field that has a lot of built-in deadlines running on short enough periods that I rarely am allowed to get so far behind that it feels like it's too much. I also have developed checklists, reminders, and organizational strategies over time that work for me. You will have different ones, of course. But the single most important factor has been that I care about the outcomes of my work, and don't want it to be poor quality, so even when I feel like procrastinating (or, more accurately, don't feel like doing a particular task), I feel a sense of responsibility toward the people who will be affected by how accurately and promptly I perform my work.
When you find the kind of work that matters to you during this season of your life, you will also find additional internal resources for managing procrastination.
