Thumb Burning When I Extend My Right Thumb I Get This Tight Burning Pain. Anyone Have Any Ideas What It Could Be?

When I extend my right thumb I get this tight burning pain. Anyone have any ideas what it could be? - thumb burning

I thought it might be carpal tunnel, but I only have pain in the thumb and not the wrists or elbows .... I wonder if I find something on it or a tendon rupture .... Anyone tried this before? I'm pregnant and I thought it had something to do, but not sure. It has been running for two weeks and is even worse!