From memory, the shot is effective for about 6-8 weeks I think. Last pregnancy I bled heavily for 7 weeks, I only had one anti D shot during that time.
I bled heavily and often in my second pregnancy and had quite a few doses of anti D, everybody is different, every pregnancy is different, and some care givers have different knowledge on the matter or methods of treatment.
OP we can only share what has happened to us or our experience, you really do need to contact your care providers as they really would be the best ones to tell you whether you need another shot or not.
FWIW my second pregnancy I had to ring the midwives any time I had a bleed and they advised me whether i needed to go in via Emergency. Going in via Emergency is how my local hospital deals with it they then send you up to the midwives.
I hope everything works out.