I think you should definitely incorporate weight training as part of your goal for weight loss. Gaining muscle is not a bad thing, it is a great thing because the more muscle you have the more calories you burn. The scale is not always great for body image, the judge is how you look and feel and how your clothes fit, not always the + or - on the scale.
If you are overweight, you are not going to build muscle so fast that it will counter-act weight loss. If building muscle was that easy we would all be ripped.
After I had twins, I did not see any real weight loss results until I stopped doing just cardio and incorporated weight training. Good luck!