A short bow and long draw length can cause finger pinch, and if it's severe enough, there's really no way to ameliorate the effect on your index finger other than changing to a longer bow, or perhaps shooting three under.
However, it could also be caused by a form problem. It could be caused by too much downward pressure on the index finger caused by drawing with the elbow too high. A high elbow causes vertical string torquing. A high elbow usually is also an indication that you're drawing too much with your arm and not enough with your back muscles. Something to check. Try drawing more with your back and keeping your elbow lower on the draw and see if that eases the pressure on your index finger. Good luck.