Perhaps try to avoid tension in your forearms and wrists.
I second this. I've had pain along the left side, of my left hand, near the fifth finger but it went away with some relatively slow practice and a good night's sleep. The next day I just relax and try to play with fluid motion and I find the pain doesn't reappear.
If I ever get a more severe pain then I'm used to, I stop practice for a few days until it's gone and I always find when I return to practice I play substantially better.
I've also gotten pain along the outer length of my arms, which I'm certain is lactic acid build-up. I believe this is like exercise at the gym, so with a good diet and enough sleep you'll find that the pain lessens and eventually disappears coupled with a marked increase in your endurance.
I've gotten pains from octaves, fast jumps, left hand trills and rapid double thirds but as I've stated above they always go away after I what I've mentioned, namely, fluid motion (no tension- relax shoulders, mentally allow hands and arms unabated fluid motion), relatively slow practice (not too slow), a good diet (not sure if this helps but I generally eat well and I've heard this recommended for people who exercise), and a positive attitude towards my playing.
I'm an amateur by the way, so you might want to take all this with a grain of salt, though I assure you, all the above works for me.