I have been trying to stick to 1300-1500 cals a day and I stay hungry! last night I broke and ate a big bowl of green beans and quite a few walnuts after dinner!
No bloody wonder you're hungry. 1300-1500 cals a day is fine if your idea of exercise is to be really agressive with the remote. But to be active? No way. Someone a few posts back mentioned resting metabolic rate - that is the minimum your body requires just to keep your body in a homestatic state. Throw biking (or walking, or any activity) into the mix, and you're going to need more calories to find the energy.

And don't get me started on the low carb thing....Carbs are good. Especially if you're active. The right kinds of cards are where your energy stores come from.