Threatened miscarriage...

Went to the doctor last night for severe cramping and back pain.. currently 5 weeks and 1 day along. They gave me fluids and took blood. Dr tells me my hcg levels don't match with how far along I am but that could mean I got pregnant later in my cycle.. she told me to come back in 48 hours to test levels again... not feeling very optimistic but hanging in there. Good luck to everyone!