Sounds like you could be over using it. You are compensating for not having the use of your left arm? Am I correct? There is a tendon at the base of your thumb, where the fleshy part is, that can get overused and swollen. It takes a good week of putting some ice on it for no more than 20 minutes at a time to help bring the inflammation down. It should feel better in no time if you rest it. I had a problem with mine when I was lifting weights. I just overused it. It tends to heal pretty fast if you take care of it.
Hope that helps.
Hi there!
Well, this could indicate an injury to the right hand as well. Possibilities include fractures, ligament/ tendon injuries, inflammations etc. It would be best to get this evaluated by an orthopedician for an accurate diagnosis and appropriate management.
Hope this is useful.
Take care!