I nannied and used many different kinds of slings and carriers for most of that time... I also injured my back doing so.
but i also managed to figure out a few systems that work well for me now... but it took a while and I have to be careful. for some bodies, baby wearing is a breeze and for others its really hard on their bodies...i've seen a pretty big mix of both.
personally i found that the sling was hardest on my body after prolonged use. mostly because only one side of your body is supporting baby's weight. also getting a ring sling to fit properly takes some practice. I've left things a bit too loose and see many parents who leave the sling too loose, and that can really pull on your neck. the bjorn was equally as hard on my neck and shoulders (no waist belt) but at least the pain was on both sides : )
a soft carrier can be great. i have an old school beco where i'm able to move the front/back straps up and down on the shoulder straps as much as i want so, while wearing a baby on my front i can buckle as low or as high up as feels best for my back. i think most newer carriers down allow for the buckle to go super low (which is what i personally need). for me the moby is also great but i can only wear it for short periods of time because the cross in the back puts too much pressure on the part of my back that hurts. basically in that long paragraph, what i'm trying to say is that you can likely find a carrier that takes the pressure off the parts of your back that are most sensitive. different carriers put pressure on different parts of your body so if there is somewhere near where you live where you can go try a ton of carriers on and get fitted AND can walk around the store for a while wearing it, that might be your best bet.
and hey, cut yourself some slack, its hard to figure out actually, i mean i've been doing it for 10 years and there's even a learning curve w/ each new baby i cary and each new carrier i try. i will say after so long it takes me only a small amount of time to get an adjustment right but in the beginning it took me a while to see why i was in pain and the ergonomics of different kinds of carriers.
anyhow, i wish you the best of luck and if you have questions about certain carriers i think you will get a lot of specific answers from the ladies here, myself included.

s