Heading to a baby shower...

Hey all, I'm just looking for someone who can relate.
Today is my sister-in-law's baby shower.
My husband and I have been TTC for two years. His sister got pregnant her first month.
 She was overweight and lost 70 pounds in about six months last year. I'm overweight and despite my best effort, I have gained 4 pounds this year. 
I've been working with my mother-in-law to plan the shower because I am happy for her.
But I woke up early this morning to do some last-minute preparation, and I found myself basically sobbing in Walmart. 
I want to be happy for her so badly. I want to celebrate and smile. But I can't look my husband in the eye. My heart is heavy, it has been crushed.
I'm just devastated.
I'm scared.
I know that TTC two years is nothing to some of you; you are far stronger than I. I don't know if I can do this for much longer. I don't know if I'm strong enough.
I try to tell myself that that's the point. That I'm being tested and I have to prove my strength.
Today I am weak.