Hey V.,
As you know I have PCOS. My husband and I tried for a year before we were able to get pregnant. My sis-in-law and best friend gave birth and got pregnant again while we were trying. I found myself thinking how unfair it was sometimes, but I simply couldn't help but be overwhelmingly happy for her. It wasn't her fault that we couldn't get pregnant, and I could just see how happy and excited she was.
When she first found out she was pregnant the second time, she didn't tell me for a while. I found out from the rest of the family. My MIL told me that she was worried about telling me and our other sis in law (they have been unable to get pregnant as well) because she was worried how we would feel about it. To be honest I was more hurt that she didn't tell me because she thought I would be negative about it.
Then when I finally did get pregnant, I was SOOOOOOOOO HAPPY!!! I was so grateful to be pregnant that I made a promise to myself that I wouldn't complain ever about it. My husband told me during my first trimester a few times that I needed to tone it down a bit because wouldn't Megan (my other sis-in-law) be feeling badly about it. It really bothered me that I would have to tone down my happiness because someone else might be too sensitive.
I know that sounds very selfish, but I had been trying soo hard, and it was FINALLY my turn, and I wasn't allowed to show how happy I was? I finally told him that I knew how she felt. Had he forgotten that that had been us only a few months ago? And yet when my other sil told us she was pregnant, I was still happy for her. I didn't hold it against her that she was pregnant, and I wasn't.
I guess what I'm saying is think about how happy you will be when it finally happens for you. That happiness is going to consume you. It's hard to think about anything else. And what if in your happiness you do just like your sister is doing, and someone were to ask you to stop making comments (that lets be honest are really to remind yourself that yes, you really are pregnant). I was actually a little upset with my husband for suggesting that I shouldn't show my happiness.
Instead of getting angry with her for her comments, use it as fuel or a boost to pick yourself up again when you feel like it's hopeless or like it's never going to happen. Have faith that it will happen, pray that it will happen, and never give up.