Possible miscarriage

I want to the er. Due to period like cramps. They told me I'm in the process of having a miscarriage.. Me and my fiance came home and prayed. I refuse to lose my baby. I'm only 3-4 weeks. I only have a sac. I'm thinking that possible and may be having a miscarriage means that it didn't happen yet. I'm trying to prevent it by being on bed rest. I've gotten bad cramps while I was working. Have anyone went through something similar? And if so how did You react? I feel like I just have to take it easy and not stress my body. #firsttimemommy