Heavy bleeding & uncomfortable cramps

My best friend is 5 weeks pregnant. She has been having heavy bleeding & cramps. At first, we thought it could be a miscarriage. She went to the doctor & the baby is perfectly fine. Urine test, blood test, & ultrasound came back & looked perfectly fine. Doctor has no idea what it could be. For now he told her she needs 9hrs. of sleep, no heavy lifting, & lot’s of water. She’s under observation & has a lot of follow up appointments.

Anybody has gone through this or any idea of what it could be?