Also, with your problems with milk supply, you'd probably increase your milk supply more by nursing baby (since baby is better at this than the pump) directly in the morning instead of feeding her a bottle and cereal.
If baby is having breakfast while she's away from you, and you can't nurse her directly then, make sure you're using the slowest flow nipples possible, and remember that while you don't like the idea of formula, that it is more nutritional than the cereal. If you have to supplement at 4 mos., use the formula instead of cereal. It's got better nutrition and good fat content. Cereal is good for practicing eating, but it's not very nutritional, and the added vitamins aren't metabolized by baby's body as well as the vitamins and nutrients in breastmilk.