Karen,
I had some major left elbow pain on my road bike with drop bars for the past year of riding. Never any elbow pain at any other times- just on riding bike for more than 15 miles, getting worse as the rides get longer.
My doctor (who is a cyclist) suggested I change handlebars.
I got a different drop bar that is shorter reach so I am not as stretched out- a Salsa "Poco" bar. There was an immediate vast improvement. The pain is not ALL gone- because reach is still a small issue with my bike.....but 80% of the elbow pain was gone immediately and has not come back. Now it just gets mildly achy on long rides, but no sharp pain.
I have a custom bike coming in a few months and I bet there will be no elbow soreness at all on that one.
You might try a bike fitting and short reach bars. I think the elbow pain is from your weight being too far forward onto your hands. You need to get your wieght balanced further back.