No exercise is a waste of time... Both strength training and cardio are good for weight loss. Strength training builds muscle and muscle burns fat.
I don't know how long you've been doing the exercise, but perhaps, your diet has been lacking the right kinds of foods or too large servings. Exercise, alone, rarely causes a lot of weight loss; diet is crucial.
Safe weight loss is 1-2 lbs/week; if you lose more than that, at this point, it's most likely it will be water weight, not fat.
I would recommend focusing on cardio exercises. Our bodies tend to react faster when we give it a variety of high intensity exercises. If you like to run or bike, try interval training. Also, eat a diet that supports your goal. Fat burners, like citrus and berries, double as metabolism boosters.