Misdiagnosed

has anyone been misdiagnosed with miscarriage? I went to the ER today and I'm only 6 weeks 1 day, and they told me I'm losing my baby. They said they couldn't hear a heart beat. But I'm not really far enough along for the baby to have one? I know I could have miscalculated my due date and I could even be only 5 weeks. I have cramps and spotting. It's can be brown, pink, or reddish. But it's not always there when I wipe. I had crazy cramps last night, up every hour and unable to leave the fetal position(which is what prompted the er visit) and I'm just wondering if they may have jumped the gun.