depression kicks in

I feel so bad for saying this... But I'm sad, jealous... Angry. I've been with my boyfriend (happily) for 4 years now. Since May of 2014 we have been having unprotected sex. We were never "trying" but we do want a kid... If that makes any sense. Anyway, 2 years later I have never ended up pregnant... I am sad. A lot of girls I know are getting knocked up by guys they're having flings with or just casual sex... But my boyfriend and I who love each other immensely... We can't seem to get pregnant. I'm just jealous and sad and angry... All in one. I'm afraid we'll just never have our own children. Am I the only one this is happening to because it sure feels like it.