Why do people feel the need to tell me how BIG I am? (Sorry so long, needed to vent :-/ )?

So I just come from the store where a sales clerk asks very happily how far along I am, when I reply "5 1/2 months" her eyes nearly pop out and she whispers, "you're BIG!!" I politely smile and say "yea", what else am I supposed to say?! Then she adds to the insult by saying "only one?"..OMG WTF??!?!?!?! Ok so lets start with 8 years ago I weighed 110 at 5'3" got pregnant and 9 months later was 60 pounds heavier!!! Totally my fault I CRAVED Carl's Jr and indulged every chance I got! My daughter was born a very healthy 8 lbs 7 oz, we referred to her as the Carl's Jr baby! Now she is stick thin. Anyways it took me 5 years to get my in gear and lose the extra weight, I LOVED to eat! So finally I dropped 40 pounds and eventually held pretty steady between 117 and 123 lbs. When I got pregnant this time I weighed in at 125 and gained a whopping 15 pounds the first trimester! I know I know! Anyways now at 23 weeks and 4 days, my last DR appt was 1 week ago, I have gained a total in this pregnancy so far between 25-30 lbs! I am so upset with myself, I am now walkin at least 1 1/2 miles at least 5 days a week, but even though I have become more voluptuous I do have a large baby belly! I'm wondering if my husband and me just make BIG babies?!?! Anyways I was just wondering if anyone else has had this reaction from people? My 8 year old suggested that I tell the next person that I'm not pregnant, which I clearly am, but it would be funny to see their reaction.