Hey SMS! Your issue could be a lot of different things. Some beginners that have a light bow hold and do guide the bow with the index still use too much shoulder/arm in the stroke. To counter this, make sure you are bending your wrist as much as possible when you are coming up-bow (from the tip/end to the frog where you are holding the bow). Try to also watch your right elbow when you play. When you are on the same string, it should only move slightly at the beginning of the stroke, and then be still for the rest of the stroke. If you find your elbow is moving constantly throughout the stroke, then you are using too much arm (and shoulder) to bow.
It is equally important to not use other muscles to bow while holding the bow. Think of the index and bow hand as your shoes tied tight before running a race—if you have them tired tight you are going to run a great race! But what would happen if you had a 100 pound backpack to carry while you are trying to win the race? The backpack has to do with the shoulder and elbow movement which has to be as relaxed as possible, and not be used to guide the bow.
The best thing you could do is post a video. I will be able to see exactly what you are doing and pinpoint how to improve. You don’t have to show your face! You can take it on your phone, post it on Youtube, and then embed it in the video feedback area. You will be amazed at how much I’ll be able to help you just by you playing a few notes. Just a thought!