usually in pregnancy
blood supply to local organs increase that may the reason for your post coital bleeding, anyhow as you are having previous history of group B streptococcal infection
and low platelet count
at present better to once get examined for present status of infection,
if test comes positive depending on your doctor's opinion you can go for treatment,
with platelet count up to 50,000,you may not have any symptoms, but if count decrease below that there is chance of bleeding, and you may need to consult your doctor once.