Is there such thing as implantation bleeding?

Yes: Implantation bleeding occurs at the time that the early pregnancy "burrows" into the endometrium of the uterine wall. It usually occurs around 6-8 days after ovulation or cycle day 21 of a 28 day cycle. The amount and color of the bleeding are variable, but it is harmless. Progesterone levels should be +/- 20 ng/ml around this time of the cycle. In repeat miscarriage check Progesterone levels..

Yes: Yes. It is due to the placenta forming and establishing itself in the uterus. It does not mean that you are having a miscarriage. It is generally very light and short in duration.