Neck question

Necks can be recarved. Best to have an experienced uke luthier assess in person as to whether or nor your neck is suitable.

Have you been playing more barre chords?
They can get crampy, esp if you're gripping too hard.

If I were you, I would not rush to re-carve the neck. Peewee makes a good point, you are probably gripping too hard. Also, it sounds like because of the shape of the new ukulele neck, you are gripping it in such a way that the pressure is on the knuckle of your thumb to a greater extent than it had been. You need to position your left hand so that the pressure is on the pad of your thumb. It may feel funny at first, but you will acclimate in a short time.

Years ago, I thought I would teach myself to play classical guitar. I struggled along on my own for a while, but eventually reached a seemingly insurmountable technical plateau. I could not play certain pieces fast enough, as fast as they were meant to be played. No amount of practice seemed to help. I decided to take some lessons. The first thing my teacher addressed was how I was holding the guitar. My thumb was wrapped around the neck too much, as I am suggesting may be the case for you now. Additionally, I was holding the guitar on my right knee instead of my left. Making those changes did feel weird for a few days, but once I got used to it, I could play faster and cleaner.

Aloha Nickie...
Here's an metaphor...If I buy a car with an manual transmission and I keep grinding gears, I wouldn't go to the transmission shop and tell them to put in a automatic transmission...It is
always cheaper and faster to get another car... sell the uke and get a thinner neck for comfort and playability...return if you can...

The real issue may be the action at the nut is too high. You might be surprised at how much even the slightest difference will affect the pressure required.

You should see how I feel when I go from playing a soprano uke, to my classical classical guitar... It feels gigantic