This is a common problem, and there could be any number of causes, including the old explanation that it's just a stage and probably won't last long. Baby patterns change often as the child grows and develops.
But, since daylight is short right now, it's possible that your little guy isn't getting enough natural daylight. Try a few days of having him near your brightest windows, especially in the morning, and take him outside for walks as weather allows (exposure to nature is also beneficial to development in other ways, too). Daylight helps regulate the brain's production of melatonin, which encourages sleep at night.
Good luck.
ADDED: Cereal is all fast-digesting carbohydrate without a lot of nutritional value. Many moms find their babies wake more often after cereals are started, both because it is digested faster than milk or formula, and because introducing new foods can cause tummy upset/gas until the child's system adapts to them.