How is your form and consistency otherwise? It is not unusual to see top notch archers wearing chest protectors, although not too common in traditional archery. I would look at your shoulder alignment and release hand followthrough, and make sure you’re not overgripping the bow. If everything checks out, you can certainly decide to open up your stance a tad, or to wear a chest protector. I suppose it’s possible that you could have been hitting your chest before and not noticed it because of the clothes you were wearing, but the important thing is that you have no doubt that you are hitting it now, and have to do something about it.