Why do moms get depressed after they have babies? Does it go away? Can dads get depressed too?

Hi, Im Gracie and I have a twin sister (idenical) named Melissa or Lissa for short and I have an older brother name Matt, he's 15 and he's a jerk (he helped me make my Yahoo! account today though). Me and Lissa are 12 but we'll be 13 in Oct. My mom left us a few months after we were born and Matt was 3 I think. My dad says that mom was real depressed, i forgot wat he called it. he said that lots of moms get depressed when they have babies especially if there're young. he said mom was 22 when she had me and Lissa and he was 25. I try to ask him more about her but he gets upset so I stopped. Me and Lissa were born 8 weeks early so we had to stay at the hospital longer than most babies, mom left a couple of months after we got out. Does being depressed make moms leave? wat makes moms depressed? do they stay depressed for a long time? can they get better? I think dads mad with mom for leaving,he doesnt really talk about her. All i kno is that her name was Amanda or Mandy, and she had brown hair and big dark blue eyes like me and lissa. matt has eyes like us but blond hair like daddy. Were any of your moms depressed? did they leave too? do you think that me and lissa are gonna be depressed when we have kids too? Dad says we wont but hes never been pregnant and Ive never even seen him cry before! I dont wanna be depressed, Ive never been depressed before. I get sad sometimes but im happy most of the time. If i do get depressed i dont think Id leave my kids like mom did. Matt says he hates mom, but matt seems like he hates everyone sometimes. It sucks, but sometimes i think i hate mom too.