I am A-Neg blood group too and I've had a miscarriage and two ectopics - the guidelines and medical opinion on anti-D injections are not clear cut. I miscarried at six weeks about a year ago and after the ectopic last August, I asked the consultant for an anti-D injection because I was concerned about future pregnancies.
There was a LOT of debate about it in the hospital, to the extent that the consultant, nursing sister and medical students were brought round my bed to discuss whether I did/did not need anti-D.
The general concensus was that it is not necessary to have an anti-D unless the blood of the baby had a chance to mingle with the blood of a mother. I was told that the circulation in the baby did not begin until 12 weeks, so unless the miscarriage happened around or after 12 weeks then anti-D was not necessary and not routinely given.
However, I was told that the consultant that he felt that it should be "best practice" to administer anti-D anyway to any negative blood group mother after any miscarriage "just in case", but that it was not common until the baby was older.
There is no harm in getting one and I definitely wanted one, to be sure - it is a small needle in the bottom and an inexpensive injection for the NHS. However, as I understand it, anti-D has to be administered within 72 hours of potential exposure to the baby's blood to be wholly effective.
Speak to your GP, although the hospital might be a better place to start.