Bleeding at 21 weeks.

We are expecting our sixth baby in June. I am 21 weeks pregnant today. Yesterday I started bleeding and went into the hospital. They ruled it as a "threatened miscarriage" because it's too soon to be deemed "preterm" if she were born now she would have no chance at survival. So I've been stricken to bed rest for now. It's been really hard because I have five young children who are home too and don't understand. Our oldest is 8-almost 9, 6 year old, 3 year old, 2 year old, and 13 month old. Our 13 month old was born premature at 32 weeks, but made it through all the NICU stuff and is happy and healthy. I was in bed rest with her too but then my water broke at 32 weeks and there was no stopping her.   am scared and wondering if anyone else has experienced "too soon" stuff like this.