All bumps are different. My first pregnancy barely showed at 31 weeks when I had my photos done. And the bump, when it came was nice & round. I worked out at my noon hours and at the gym on weekends until the 7th month of that pregnancy. This time, 8 months after delivering my DD, I'm pregnant with twins. I worked out for 3-4 months before I got pregnant again but my muscles are definitely weaker. I had 2 subchorionic hemorrhages in my 1st tri that prevented me from working out and my bump starts with a big fat roll from my side this time
Your shape is determined by how tall you are (I'm 5'9) how you carry, and how much fat you have on your body. I'd guess you're 18 weeks. Am I close? I tell people I'm proud of my beer belly. You can only do this for so long until the big round bump will appear.