Are there two switches, one for the light and one for the fan?
You most likely have three cables entering the box: one set (b/w) is the hot feed in, one set (b/w) is the feed out to the receptacle, and the other set (b/r/w) is to the switch. You will need to determine if this is correct and identify each before proceeding. (Note: each cable should also include a bare or green grounding wire).

This situation is likely to require significant elecrical expertise. Randomly connecting wires can create a potentially hazardous situation.

You may need to conduct tests using a multimeter to determine which wires provide what function. If you don't have any experience in that area, I suggest you get a copy of Wiring Simplified from your public library (or buy it at a bookstore or Home Depot store). Study the introductory section on basic electrical circuits especially well. Then you'll be in better shape to tackle this problem.

If that seems like too much effort for one small fan installation (which would be understandable), then maybe it's time to call in a pro.