Glad to hear about your improvement and that you're committed.
You have to find the right amount of tension in the arms. We're trying to just maintain our radius on the backswing and until after the ball is gone. Now, if you didn't know, the back arm (right arm for a right hander), does bend some on the backswing and then on the follow through the left arm will bend after the ball is gone. What we are trying to do is keep the arms close together so they work as a unit. If you have relaxed arms and elbows, the radius changes... usually with collapsing on the backswing, then elongating (stretching longer than setup), on the downswing due to inertia. You don't want the arms stiff as possible. You just want the elbows working towards each other. It just takes practice to find the right amount of tension. Also, the elbows pointing at the hips at setup and through impact really helps too. I don't want you to hurt yourself. I think most people know the difference in sore muscles from a new use or exercise, and doing something wrong that is causing pain. You may be just over doing it a bit because your'e having fun. You have to be the judge on this. If it does not improve or gets worse... you should make a change.
Move Less ... Get Good! DUPLESSISGOLF