Thumb pain

Which thumb? Fretting or picking hand? Which joint?

Which thumb? Fretting or picking hand? Which joint?

sorry I forgot to specify fretting hand, the joint closest to the palm

It sounds to me like you are Likely Gripping your Guitar too hard which in turn will cause not only Pain but Permanent Damage to your Hand and Arm. You should only use the Thumb to Hold your Guitar from moving backward when you Fret a Note or Chord. Apply Just Enough Pressure to the String to Sound the Note or Chord Correctly. Too much pressure will also change the Note or Chord out of Tune (Sharp or Flat). So try to find the Minimum Amount of Pressure you can use to Sound the Notes Correctly, that will also Relieve the Stress and Pain on your Thumb. Hope this Helps.

It sounds to me like you are Likely Gripping your Guitar too hard which in turn will cause not only Pain but Permanent Damage to your Hand and Arm. You should only use the Thumb to Hold your Guitar from moving backward when you Fret a Note or Chord. Apply Just Enough Pressure to the String to Sound the Note or Chord Correctly. Too much pressure will also change the Note or Chord out of Tune (Sharp or Flat). So try to find the Minimum Amount of Pressure you can use to Sound the Notes Correctly, that will also Relieve the Stress and Pain on your Thumb. Hope this Helps.
Thanks a lot I appreciate you taking the time time respond. It's weird I feel like I need to press with my thumb, so I should be feeling the pressure in my forearm?

You should not feel Pain Anywhere. The most you should feel if you were a Beginner is a little soreness in your Left Hand since you begin using muscles you haven't developed and maybe a little pain in the fingertips. I have always played in excess of several hours at a time (Not Solid) with very little pain. The fingertips get sore but that passes over a few weeks, let them rest for a day or so then go back to Practicing.
I feel like you may be using your Arm to fret the Strings and you should be using the muscles in your left hand with a Relaxed Arm. Try to get a feel with your fingers, just How Little Pressure it takes to Fret a String. Kids can do it so that goes to show that it doesn't take much Strength to Fret a note. Use "Just Enough Pressure from your Fingers to Fret the Notes and see what you get. If it is taking that much pressure to Fret a Note, you need to go have your Guitar Checked out, your Action is too high or something. Use your Thumb ONLY as a Brace to keep the Neck from Moving Backwards when you Fret a Note....that's All. Try that and see if it helps. Let me know how you caome out.