I had a wedding to go to 11 days after DS2 was born. I wasn't fit for anything other than sitting there not budging and smiling at others brooding over him!
Even though I had a natural birth, I had a second degree tear. Sitting was uncomfortable and when I walked, I looked like I had been riding a horse for over a decade! I ended up leaking blood on my white skirt, and my boobs were leaking so much, I was having to keep changing my breast pads every 10 minutes or so! And although I barely saw DS that day as everyone kept nicking him, I was still very uncomfortable and wished I hadn't gone. But DP was an Usher and I didn't fancy being stuck at home on my own.
Trust me, on the day, you will be glad that you aren't a bridesmaid. Especially if you tear, need a c section or go overdue.
I can understand that it has upset you, especially if it is mainly because they are worried about your weight and not to do with the dress (which I think is most likely to be the latter). But I understand where they are coming from, too, if it is the latter. My sister in law to be got pregnant, and she is one of my bridesmaids. She would of had the baby shortly before the wedding and it was causing a right headache trying to find a dress they all liked and she would fit into on the day. Plus bridal shops like to order the dresses in 3 months before the big day, and she would of been heavily pregnant. How on earth could we guess what size she would be? We couldn't. But we had to postpone anyway, so it worked out in the end. So long as she doesn't go getting pregnant again! I think I will cry if she does lol.
Chin up, try not to take it to heart. And congratulations on your pregnancy!