Bike fit is not a clear-cut science; you need to be comfortable, and that may mean moving away from certain of the unbendable rules of bike fitting. You may indeed be stretching too far, and consequently carrying too much weight on your arms/hands/shoulders. That could always be exaggerated by having core muscles that are at less than optimal strength. Your bike may be a little too big for you, but changes in stem, seat post layback, etc. should solve the issues. Instead of giving people £75 to tell you what you already know, try a few changes (one at a time) and just listen to how your body talks to you.