Taylors have a thinner neck profile than Martin or many other acoustics. In a similar budget range to the Seagull is the Big Baby Taylor. I have one and really like the thinner neck - feels more like an electric. Or - if you really love that Martin you could have a luthier shave the neck to a thinner profile and then refinish it
David's sports medicine person made a really good point about looking at your hand position when playing. Repetitive Strain Injury (and that is the diagnosis that we are probably talking about here) is all about the cumulative strain on tendons, not the bones and joints. It is worth knowing a little bit about the anatomy of the hand and wrist.
The muscles that move your fingers are all located in the forearm. Put your arm and hand (palm down) flat on the table and drum your fingers up and down. See the muscles moving way up near your elbow? They are attached to long cable-like tendons than run all the way down through the wrist, to the finger bones. If your arm and wrist are in a neutral position like they are on the table in front of you the tendons have a pretty straight run from muscle to bone. But if you bend the wrist, rotate it, add some lateral angulation - now those tendons are running around some corners and experiencing some real friction. When you are playing you might hold your wrist in that position for an hour or so, and put significant tension into the muscle/tendon unit by holding down a bar-chord on a steel-string acoustic. It is no surprise that guitarists get some trouble.
Like typists and machine operators - it really makes a difference if you adopt the most ergonomic position. Often our playing style sees us develop some unhealthy postures.
I hope that it all settles down for you.
Even though im 16 i snapped both wrists in two past sports and as for my fingers i am still good so would finger exercises help keep my fingers in tip top shape too ( i do use finger exercises though cause i play thrash and heavy metal).
and the acoustic had a nice thin neck and medium tension it was a taylor customs i wish i could find it again cause that thing was comfy on my hand ( in got stolen from my back stage rack 2 years ago)
You've gotten lots of good medical advice here. Let me add a few comments on the instrument itself.
I would look at the setup of the guitar. A nut that is too high will cause you extra stress in the first position. And the amount of neck relief and saddle height will also affect the instrument's playability.
Then you might consider a lighter gauge string.
If after all of these you still find pain, it may be that the guitar is not one that fits you well. You may want to try others.
Whatever you do, get the problem corrected. Lasting pain from performance is something you need to address or give up playing!
And perhaps take a lesson or two from a serious professional teacher. Sometimes we develop bad habits that we don't even recognize and a good teacher may be able to identify a problem with your technique.