New wrist problems

Some of this is likely due to higher tension, rougher strings. Make sure your left and right hand technique are ergonomically sound. If you correct those things and you still have problems, you may have what I have, which is a pinched nerve/back issue radiating down into your arm and hands/fingers. It put me out of commission for a good 6 weeks.

If your technique is perfect and this doesn't go away or gets worse, you'll absolutely need to see a doctor. If it's tendonitis or carpal tunnel you'll need an orthopedist. For a nerve issue, find a good neurologist.

 

Stop playing bass for a few weeks to let the inflammation go down.

When you pick it back up, limit playing to an hour or two a day and focus on keeping wrists straight.

As strength builds, the muscles will protect the fancy parts underneath.

Or see a real doctor. What do anonymous people on message boards know?

 

Is your left hand set the right way, or are you jumping on some of those frets withyour thumb?

 

The bass requires a different technique approach from the guitar. Try to keep both wrists as straight as possible. The sore thumb on the left hand is probably due to pressing down too hard to fret a note. Links for left and right hand technique below.

The sore fingers of the R/H could be from plucking too hard and/or the fact that your fingers are not used to the stronger, larger strings on a bass. Use a lighter touch and bring up the volume on the amp to compensate.

R/H :

Todd Johnson Bass Guitar : Floating thumb technique - YouTube



L/H :

Beginner Bass Guitar Lesson: Left Hand Technique - YouTube


Developing Safe Left Hand Technique for Bass Guitar - YouTube