Welcome, Libra!
You're still very young and have plenty of years to train in whichever career you choose. I know plenty of people who get interested in medicine right as they're finishing up college, and they go for a post-bac degree. So don't worry about it at all. PA and physical therapy are great medical routes (i've particularly heard great, family-friendly things about physical therapy). It's great that you're volunteering, but since you're not sure if you want PA or PT...you should reach out to some people in those particular fields to get some shadowing experience. Of all the volunteering I've done at hospitals, I spend most of my time observing the nurses.. they're just the ones who are there the most, doing the grunt work. So unless you're interested in nursing, volunteering in a hospital is more of a broad exposure to medicine (which is great to continue doing, but you need more specific experiences as well)
Maybe if there are any PA's or PT's on here they'll chime in to say what those careers are like from the mom's perspective.
Also, if your only reason for not choosing to pursue an MD is because you can't support yourself in medical school.. then you should rethink that! You mention not having kids and I'm going to assume you're not married... if so, you represent the majority of students who enter medicine. Med students live frugally and take out loans to support themselves, so that shouldn't really be an obstacle. If you're married then you are even better off! I can understand if you don't *want* to live that way (taking out loans, etc.) but if you really do want an MD, that's not something that should stop you.
Good luck on your journey and keep us updated!