MichaleW may very well be on the right track in regards to poor saddle position!!!!!!!

You may be putting pressure on your hands/arms and holding your arms striaght, to keep from sliding forward on the saddle. Are you riding with your saddle "nose down"?
If so set it to a LEVEL position, ( or very slightly "nose up"), to keep from sliding forward on the saddle, many experts actually will use a carpenter's level to get the proper angle . It is VERY IMPORTANT to have your saddle LEVEL, it will prevent the injuries you are now getting! You will need to learn how to ride in, ( adjust to) this position. You may need to consciously tilt you hips back a bit until you get used to the new position.
Very often the need to ride with a "nose low" saddle is a symptom of a "too high" saddle height!!!!
One of the first things a good coach will do when he gets a new team, especially juniors and novice racers, is check the positions of his riders, I know of no coach who will allow his riders to ride "nose down".
Once you get your saddle level you will also need to learn how to hold yourself up with the muscles of your trunk, after you do that you will be able to ride with only the weight of your hands and forearms on your bars, AS YOU SHOULD!!!
Stretch you low back, glutes and hamstrings so you can ride in a lower position, this will help you ride with arms bent and the lower positon will give you more power as your glutes are more efficient in the lower position.

Ride Leveled
Pat