The jealous sister

Charlene • I`m from a small town, and me and my hubby got married march 2013. Hoping for a miracle:) <3
So right now both of my sister in laws are pregnant (both for the second time back to back) my one sister in law has a boy almost 2 and due with a girl in June and my other sister in law has a boy 14months and is due end of April.... This is amazing as I love my nephews and I genuinely am excited for them.... However, hubby and i have been trying for just over a year with no luck and they both got pregnant either the first or second time by pure accident... The one is constantly trying to give me tips and advice and I have even asked her to keep that topic as an off limit thing to lower my stress but she can only seem to do that for a week tops.. (She's my BFF too so this makes it hard to tell her how I feel) we recently went to a birthday party for a two year old cousin and without over-exaggerating me and my husband were literally the only people their either not pregnant or had a child under two... It was awful, all I wanted to do is cry and I was miserable because that's what they talked about the whole time. I tried to change sl the topic a million times and it always circled back to being a mom and pregnant... It's getting so bad I can't even be around them anymore.. The one who is due in June is really bad for never wanting to talk about anything else but her pregnancy and I've even told her that it makes me uncomfortable and sad, hell I broke out in tears once and she still doesn't get it... I hate feeling like this towards them, what do I do?