How do people breed guinea pigs and there girls don't die?

i had a girl and i wanted her to have babies( for me to keep) but 1 day after she had 1 baby she died and i had to feed her baby boy and he was doing really good he even made friends with one of my other males and he was the biggest out of them all and he was the smallest but for some reason he died when he was about 3 weeks old i don't know why he just didn't look so good and we got a appointment at the vet but it wasn't till the afternoon and then he died about 5 mins after we the called the vet about appointment but anyway why did she die? ( and she still would of had more inside but she only got one out) and how do other people's girls don't die? (also i wanted to breed cuz when ever i get a guinea pig they are really scared and don't like to be picked up and if i was there when they were born they would liked to be picked up and like people)