Christina- I wonder where you lost weight from if it wasn't at least some body fat. 7 pounds would be more than just normal variation due to hydration, etc. I believe body fat is somewhat fickle and difficult to measure accurately other than hydrostatic weighing (underwater weighing) (
http://www.annecollins.com/body-fat-calculators.htm). I am guessing you have lost some body fat, you just can't detect it yet. For example, if a guy weighs 150 lbs and has 25% body fat, then he has 37.5 lbs of fat. If he loses 5 pounds of fat, he would still have 22.4% fat. The difference between 25% and 22.4% is likely within the variation for your measuring equipment.
Bottom line- keep exercising and you will see a difference. Exercise plus appropriate calorie intake will result in weight loss.
As for weight training or low impact exercise- I do not know so cannot comment if they will specifically help. I would guess that calories burnt are the same whether fast/slow, low impact/high impact. You would just burn them faster with higher intensity workouts. Also, muscle burns more than fat, so increasing muscle mass (i.e. weight lifting) may help you burn faster.
I can't really help you from experience, since I have like no body fat
Steve- That's not real helpful or empathatic. A bit more tact would be polite.