Not to sound discouraging, but I see a couple red-flags after reading your post. First of all, I am thinking mainly of in-patient nursing as that seems to be what you are considering. Being a nurse can be pretty physically demanding, and I am not just talking about "running around." I'm talking about lifting, bending, pulling, etc. I am 23 and I come home physically exhausted. Thankfully I have no sports injuries from when I was a teenager, but my knees are already bothering me. I should probably invest in some better shoes.
On the plus side, as someone who has pre-existing injuries you might be a little more adamant about using the proper man-power/equipment than a young (stupid?) person like me. You might also be able to work in a field that doesn't involve as much lifting (peds, ob, psych?), but it all depends on the job market.
Which brings me to the next consideration. Look into the job market in your area, and try to get a feel for what it is going to be in 4 years (depending on the degree you pursue). Spend about 20 minutes on the board, type "job market" into the search box, and you will see that nursing isn't the holy grail of the current job market. You aren't guaranteed a job, it isn't "recession proof," and you can't work wherever you want. I am lucky enough to live in a city which had its "depression" about 5 years before everything else hit the fan, so right now we are doing pretty well. I'm not saying you shouldn't go into nursing, just do some serious research before you go into debt for it at this point in your career.
As far as nurses being "errand boys," that certainly can hold true, but it depends on your personality. I was pretty much the easiest person to walk-over/manipulate before nursing school, but between nursing school, a job as a tech, and a year and a half in the field, I'm developing thick enough skin to stand up for myself. When I was a tech I let a doctor come out of an isolation room, find me on the other side of the unit, and ask me to take a patient's temperature because they looked feverish (the thermometer was at the patient's bedside, and they didn't have a fever). If that happened now I would kindly bring the doctor into the room, show them where the thermometer was, and possibly ask if they needed help with anything else. If you are professional, most people will treat you professionally. If not, it is their problem
I can't really shed any light on the RD vs. nutritionist question, but I wish you luck as you decide where life will take you next!