Feeling bad about pregnancy because SIL..

Katie
I realize that this may offend some people and I'm sorry...that's certainly not my intent. However, I'm pregnant and due on 12/21 (9 days after my son turns 2). I also had a m/c in October. So I guess that makes 3 pregnancies in two years...technically. 
So my issue is this... My husband's brother and wife have been TTC for over 5 years. They're pretty open about it and my SIL actually told me the night of my wedding to start trying immediately because it takes so long.
The problem is now that she knows about this pregnancy...she's been saying that we are selfish for having more kids in front of them when we know how hard it's been. I don't feel that I've done anything to "flaunt" my pregnancy. I very much love my son, as any mother would (I hope) and we are cautiously excited about the new addition to our family (I lost last baby at 10 weeks)...am I being insensitive? To be honest, I feel as though she's being unreasonable to me and it's really making me upset.
So I guess my question is this - what is the expectation when someone close to you is experiencing infertility? I recognize the pain they must be feeling...but I guess what is my role in that? 
Any suggestions or advice welcome. I'm sorry if I upset anyone.