I say mouse or trackpad overuse.
But I'm guessing if the OP is lefthanded, they mouse/trackpad with their left hand, not right.
Actually, and I can't believe I never noticed this before, I tend to use the trackpad on my laptop with my right hand. Which is weird, because I definitely use my left hand for everything else. Marigolds, I've been working a lot on the laptop since I have two major grad school assignments due, so I bet you're right! At least, it's far better than thinking I have contacted some rare disease.