Not too surprising. It takes time to develop your body's ability to produce energy from stores. Long time riders don't need to eat anything before a ride of less than 2 hours, but beginning riders can't do that - eating a little before the ride, mostly carbs, then then continuing to eat a little maybe every 1/2 hour during the ride will be a big help. Bananas, bagel, sports bars, gels, shot blocks, sports drinks - there are about 2 zillion choices, but keep it mostly carbs on the bike. But don't eat too much, either! That'll make you logy and then fat. Keep it to 25g-50g carbs/hr.