Another big question is for how long is the OP riding? I think most of us, when starting new fitness routines may think we are burning more calories than we actually are, when really we aren't going long enough and at an intensity to produce really big results.

A real life example: over the summer my wife and I went on a 14 mile ride, took us around 1:15 to do it. I use a power meter, so I get my work in kJ, which roughly translates into calories. So for that ride I expended 270 calories, not really a lot when you think about it, so you'd have to go on around 10 rides like that to burn a pound. When you're new, like my wife is, it's going to feel hard, but that doesn't mean you're getting dramatic results. It takes a lot of work; I know, I lost 60lbs through a combo of cutting back eating, increasing the time I spent riding plus increasing intensity to burn more calories. So, while an hour plus ride with my wife at this time will only burn maybe 200 cal/hr, I can ride at a reasonable pace where I burn 600 calories in an hour (and if I'm at "killing myself pace" that number could be 760)

best of luck!