First, I would stay away from a combination weed and feed. Combinations just don't work that well. To stop weeds before they start growing, you use a preemergent herbicide. Corn gluten is a natural non-toxic product. After the weeds are growing, then you need a post emergent herbicide. You might end up using a broad leaf weed killer, like Ortho's Weed-be-gone, but they are toxic. I stay away from weed killers as much as possible. If you keep your soil fertile, mow high and mow often, the grass can choke out a good number of the weeds, but you will always have a few. I pull those or leave them.
EDIT: Is your soil compacted? Grass doesn't like compacted soil, you may need to aerate. Sprinkle compost around frequently too.
