Almost certainly you're dealing with inflammation of either connective tissue (tendons, sheaths, ligaments) or nerve tissue. It probably results from traumatic or over-use injury... and it's probably de-generative (it won't ever heal back to it's completely healthy condition).
Some of us are not young anymore and the abuses of a hard working/athletic life are catching up. Those injuries are easy to aggravate now and once inflamed, it refuses to ease up without long rest (months). If you can get the inflamation under control you can get the pain under control.
Try anti-inflammatory meds. Take enough to actually do some good, that is, take'em every day with meals; two, maybe three times a day. A friend turned me on to naproxen (Alleve) and I started taking 440mg with every meal... it worked... except it got so that I couldn't eat without having 1/2 hour of nausea after a meal or snack. Before that, I used Ibuprofen when I was having a lot of trouble. Now I'm trying it on a regular regimen like I did with the naproxen... it's working and so far, no nausea. When I say it's working, I mean the pain is acceptable, it's not gone by any stretch. I wake up tight and hurting every morning but once I get to work I don't notice it anymore until the next AM.
The pain you describe does sound like CTS... does it keep you awake at night? If it does, you have only two choices, months of rest, or surgery. From what I;ve heard about the surgery, it's not too bad and it does fix the problem... but it will sit you out of work for a long rest. I've had CTS but not so serious, I changed my work habits, especially the ergonomics of how I worked and it went away... that wasn't tree work though, it might not be so easy for you.
CTS is, for the most part, a result of hand/wrist angle. Working with your hand bent down or up up most of the time will result in an abraided and inflamed sheath (I think it's a nerve sheath) in your wrist. The straighter you can keep your wrist, the less you will aggravate the abrasion... and maybe it can get better.
I'm not a doc or anything, but I was trained in ergonomics to prevent CTS at my last real job (not climbing related) which was a long time ago... that and I've had tendonitis from rock climbing and paddling about a zillion times... so, take that for what it's worth... which is not a lot.
Good luck... try to get some health insurance... a lot of men start to fall apart in their 50's... you don't want to go through that without some health care resources. Women's health insurance is expensive when they are young and cheap when they get old... men's is the other way around. It's based on how likely you are to use it.