i agree with the others in that yes, BF'ing helps lose weight faster - however not necessarily all of it. Like many others, I lost most of my weight while bf'ing (in combination with some moderate exercise like stroller walks!) during the early months, but it slowed down after about the 4th or 5th month. After I weaned my son (when he turned 1), I lost the rest of my weight. Again, I was workign out (not strenuously I admit) and trying to 'eat right'. Chasing him around probably helped too! ;)
When he started solids, it didn't make a difference in my weight, although it DID make a dent in my milk production. I pumped, but it's simply not as effective as direct nursing. That might be also why my period came back (around 10ish months).
Your body just might need those extra 10 lbs so that you can breastfeed.
You sound like a healthy person, active, etc, so don't worry about being classifed overweight.. that scale is different and not reflective of someone who is nursing. These general 'scales' are just that. General.