Working out = eat more.
Depending on the workout, you may gain weight(muscle weight is heavier than fat weight.)
If you are eating the same number of calories and losing weight, then it may be fat weight to begin with, then you may gain weight afterwards, from muscle weight.
Cardiovascular is better for losing fat, but working out will get you muscle(which may make you heavier or stay the same weight)
But as the first few words, working out means you need to eat more to recover the calories you burn.