Sorry - don't believe you! Are you sure your diet is just 1250 kcals per day, because that's not enough to maintain body weight let alone gain. In fact if you are riding hard that's less than you will be expending on your cycle rides alone.
If you have a good diet and are not overeating, then the one thing you need to be aware of is that because of your body's demands when cycling you'll have increased the amount of water your body is carrying.
