Originally Posted by Carbonfiberboy

When you are seated normally on the saddle, hands on hoods, get low so that your forearms are horizontal. Your elbows should be in front of your knees as you pedal, but wth not more than a 2" gap. That's a simple test.

Most likely, your core is weak. The bike is actually good core work, but as you say, you've overworked it because you don't ride consistently. The simplest thing to do is buy a copy of Core Advantage and work out with it for 1/2 hour every morning. Start at the beginning and gradually work through it over a year's time.