20 week weight gain

Rebecca
I normally weight about 155-158. But when I got pregnant I was weighing in at 168. I knew I wanted to be mindful of my weigh gain, hoping to slim down while baby was growing. But I haven't changed my diet, and I haven't gone to the gym once. I assumed by now I would have gained something. But I'm almost 21 weeks, with my 3rd child, and I still weigh 168. I hardly even look pregnant. Is anyone also experience this? How much have you gained thus far? Are you showing yet?