Multiple rhogam shots

So I am B-, boyfriend is not sure of his blood type. I received my first rhogam shot at 5 weeks, they thought I was miscarrying and bleeding stopped.

I am currently 13 weeks and bleeding and dr is sending me for another rhogam tomorrow.

I’m wondering has anyone had multiple rhogam. I always thought you got it halfway through and then after delivery but my dr said the antibodies can wear off after 8 weeks.

Of course I trust his opinion and will get the shot but I guess I’m looking for advice and positive outcomes.