I feel the same way. I was trying just as hard to convince myself i was happy for other people as i was trying to convince them. You just have to be honest with yourself, even if you are lieing to them. And as horrible as it is, that is the truth...i'm just not happy for people who can get pregnant at the drop of a hat. I don't go to babyshowers. I just tell them i have a prior family commitment, apologize, and send a gift. If that makes me a bad person, then so be it. No woman who is struggling through infertility should have to sit through someone else's baby shower.
When my best friend got pregnant, i had to take a step back from the friendship for a while. She completely understood and gave me some space. She had PCOS and some other problems, so she was prepared to have issues conceiving, but she got pregnant on the first month. I think that made it any harder.
I don't even talk to anyone about it anymore unless i know that they have been through something similar.