Threatened Miscarriage

I'm about 5 weeks along and I went to the ER yesterday due to some spotting and cramping. They did an ultrasound and Doc said they didn't get a heartbeat so I have to do a follow up with my OB next week. When I got discharged, they said I have a threatened miscarriage so I'm on bed rest till I see an OB. Anyone else had a similar experience? I'd love to hear about it. Kinda worried but the nurse said it might be too early to hear a heart beat which is why I'm having a follow up to check on my blood and what not. This is my first pregnancy so I'm new to all this. >.<