TTC & Sister's wedding in Bahamas

My husband and I of 3 years are TTC. My sister has decided to get married in May of 2016 and I am her matron of honor. 
My delimma is she has blaintenly told me that she doesn't want anyone pregnant or fat in her wedding and that I should wait until after her wedding. Her excuse was so that I wouldn't hate the photos of me. Really!?!?!? 
Now I get it, it's her day, but if we conceive soon I will have to choose between going to her wedding and leaving my less than four week old child at home or waiting to start our family. 
My husband and I are beyond ready to start a family and I feel like I have to post pone that for hers. 
Am I just being selfish?