Hi! Dr. I' M 22 Yrs Old My Maternal Status

Hi! Dr. I' m 22 yrs old my maternal status is 6 mnths .this is my first pregnancy .I,' m 17 weeks now.during my 12 week scan everything seems to b normal bt in 16 week when my usg cervical length was done it is found that my placenta is lower lying which was normal during the 12 week .my midwife had advice me for complete bed rest ,no travelling,no steps ,no sex .will my placenta move up as I take rest & other precautions & if not wt complications would I & my baby hve to cope up with pls advice