thanks for your query.
Considering that you had previous 3 CS, I personally would not advise you to go for VBAC, as the risk of scar rupture are quite high.
Also, The low lying placenta might be just a low lying placenta in other women, but for you , with three previous scars
on your uterus
, especially if the placenta is anterior and low lying, the chances of adherent ( placenta stuck to previous scar ) is very common, and is life threatening condition.
Also, by the 7th month, low lying placenta generally migrate upwards, but if it persists, I would advise you to go for elective LSCS, specially as you have already had 3 adverse pregnancy