DDH, you might like http://caloriecount.about.com/. I've used that site to lose weight, and now I'm using it to track my biking (not that I couldn't still lose weight, mind you!).

The tools on that site can be used to figure out approximately how many calories you burn per day (by inputting your weight, height, and activity level), log your food, track your biking, and see how much your daily deficit is -- the difference between what you burn and what you eat. A deficit of 500-750 calories a day is most effective for weight loss. (A lot of people think the bigger the deficit, the better! But that isn't so, and too large a deficit is counter productive.)

Concur with all others re: recent weight gain. You'd have to eat 56,000 EXTRA calories to gain that much weight, an extra 1,800+ per DAY, every day!

Please talk to your GP about this. You might want to have a friend go with you to help you advocate for the testing that you need.

Good luck!