Generally speaking, an index finger that is sore on the inside is caused by pressing down on the nock of the arrow as you draw the bow. In addition to the discomfort, the downward pressure of your index finger causes a bend in the arrow shaft, which will spring back up when you release the arrow. This results in erratic arrow flight and makes it impossible to accurately tune your arrows for correct nock point location.
You may be holding your drawing elbow too high, although there is nothing wrong with starting the draw with a high elbow as long as it moves back down as you draw the bow so it is almost in line with the arrow, if still a bit high, at full draw. Basically, your goal is for the force of your draw to be in line with the arrow, with no pressure in any other direction.