How long does a low lying placenta usually last? i'm only 11 weeks pregnant is it possible i may have to go 7 months without sex?

Unlikely: It is misleading to diagnose placenta previa or low placenta prior to mid-pregnancy, as the placenta is large relative to the surface area of the interior of the uterus early in pregnancy. I would make recommendations regarding the placenta, such as vaginal rest, only after the mid-pregnancy (18-20 wk) ultrasound. If diagnosed then it would be prudent to wait 6wk or so to recheck for resolution.