Can't help jealousy

Becca.
We've been TTC almost a year and a half now, everytime I've seen on Facebook or friends announce births I've genuinely been happy for them.. However, as the new year approaches, this morning we heard our best mans wife is pregnant again with her 3rd, easy peasy, have sex and 'hey presto!'. And all I feel is bitter, and jealous.. Why aren't we getting pregnant with our first?! 😔
Anybody else have this issue with dealing with these emotions? 
Xx