Yep, sounds like it's your bike fit. You are most likely leaning too heavily onto the bars. Best solution is to ask around a few bunches and find a fitter with a good reputation.
Chances are you have your seat too far forward and your bars too far away. Look at your saddle setback, you may have to increase it so that you are encouraged to put more of your bodyweight back onto the seat. This can benefit your riding anyway by encouraging you to use your glutes more.
Your stem may also be too long, forcing your bars away from you and encouraging you to put more weight onto your arms. You may have to consider shortening your stem and possibly also lowering your bars in order to relax your arm/shoulder angle without changing your back angle.
Sorry if any of this sound counter-intuitive, but these are mistakes that many people make when they are new (and not so new too) to the sport and have never had their bike fitted to them.
Last edited by 42x16ss; 01-28-12 at 08:53.