Testosterone treatment is making me lose weight, what do i do?

Go see your doctor: I doubt that testosterone replacement therapy, by itself, will cause you to lose weight. However, if you change your eating & exercise habits for the better, this may lead to fat loss, potentially in excess of muscle gain. Rather than focus on weight per se, focus on body fat percentage. Regardless, if you're worried, it's always best to talk to your prescribing physician about your concerns.