I started experiencing similar forearm pain a few years ago. The split keyboard seemed to help a ton. I also programmed[0] an Arduino with two foot pedals. Left pedal for CTRL, right for SHIFT, both for ALT. Worked wonders. I mostly have the pain manageable now, but it still flares up sometimes, and it was really scary there for a while wondering if I might have to stop programming. To you young guns out there, an ounce of prevention truly is worth a pound of cure. Invest in an ergonomic setup and stretches/exercises now, and don't push yourself into pain while typing. Take more breaks. Once you push your body over the edge it may never quite be the same.
[0]: https://github.com/anderspitman/ergo-pedals