I can only suggest that you work on knitting looser and try different ways of holding the yarn. It all comes down to personal experimentation and coming up with what works. I think you said you use bamboo needles, more slippery needles might help. The point is to reduce the strain on your hands in any way you can. If you've not tried the Portugese knitting, you might give it a go. My hands are feeling stiffish this morning so I think I'll wash dishes by hand before I knit today.
I should never overestimate my basic arithmetic skills.