Depending on where your body naturally stores more fat, it can affect appearance versus actual weight. For instance, if two people of the same height and both weigh 150lbs. but one’s body distributes fat more evenly across the body while the other’s body stores it around the stomach and thighs, the person whose fat is more evenly distributed will appear thinner than the other person. This can also be responsible for a fluctuating clothing size and why you might find your shirts fitting looser but your pants fitting snugger, etc. Unfortunately, where your body chooses to store fat isn’t under your control nor can it be manipulated, and the same goes for where your body loses fat quicker while working out.
So, the answer to your question, why do I weigh more than I look, it’s because of how your body distributes fat.