Could be any number of things, all related to your technique, IMO.
String elbow too high? Uneven pressure of your fingers on the string? Short bow with too much string angle at full draw?
OR, most likely IMO is, too much tension in both the bow hand and the string hand/forearm. IF the string makes an "S" turn as it rides on the fingers at full draw it could be putting most if not all the pressure on the ring finger. To test this, draw the bow, then really relax your bow hand. Does the bow want to turn like a propeller? If so, your bow hand AND your string hand needs serious work.
General suggestions, as we can't see what you are doing without a video.
Arne