Why do groups of women that are friends seem to get pregnant all at once without planning together?

I’m really curious as to why 7 of my friends are pregnant. These girls I met through my boyfriend (his group of friends). They are pregnant on their first or second kid…seriously! SEVEN! One is 8 months, the other 6 months, the other 3 months, one just found out she is pregnant at 2 months, the other is close to popping her baby out, the other is 4 months. One is trying to have a baby and “trap” her man which I think is really stupid, she wants to get married and is tired of waiting for 4 years although they seem happy. The other couple is trying to get pregnant but she can’t and it sucks because she’s been told she has a high chance it is unlikely so she’s watching everyone else get pregnant except her.

We’re all around the same age 24–29. I am the ONLY one that isn’t pregnant or doesn’t have a kid and I honestly feel a bit left out. I do NOT want a child right now but all they talk about is their bellies and babies and I can’t relate. I feel “behind”. Do you think they all subconsciously planned this some how? How is it that all girls are pregnant the same time?

We did have a long winter, do you think it had anything to do with that?