Low lying placenta but can't find it..

Anyone ever diagnosed with a low lying placenta, but they couldn't find how low?
My 19 week scan they didn't get any measurements, all my Dr was able to tell me was that my placenta is low lying & my cervix is short. I just got a phone call saying they can't see how low, so now I'm on bed rest & pelvic rest.
Has anyone else experienced this?
I have an ultrasound again next week.

I have marginal placenta previa, well as of 4 weeks ago (I've known my placenta was "low lying" since 17 weeks), I have my follow up ultrasound tomorrow at 29 weeks
I don't know the measurements of how low it is, but that there is till room on the cervix so I'm not on any type of restrictions.I also have a long cervix so maybe the length of your cerix in combination makes it more of a concern? You have PLENTY of time for your placenta to move(stretch) up though!

My placenta is low lying.. they said the end of my placenta is right next to my cervix.. i'm on pelvic rest as well, but because i have incompetent cervix & a cerclage.. they told me not to worry about low lying placenta because the bigger the uterus gets it'll pull the placenta up and away from the cervix.