You are having breakthrough bleeding which is any bleeding that happens when a period is not expected.
Implantation bleeding or bleeding when ovulation happens are just two of many, many, many reasons that breakthrough bleeding can occur.
If it is implantation bleeding, then you have actually already ovulated and you would get a positive pregnancy test in about one more week.
If it is ovulation bleeding, then you could use an ovulation test to confirm ovulation.
If neither of those events are happening - then it is just random breakthrough bleeding for no particular reason which can happen at anytime during the cycle. Most of the time, it is harmless and may or may not occur during each cycle.
If breakthrough bleeding becomes a regular problem each month or becomes heavy bleeding between periods, then a doctor might be able to find a cause. Things like polyps, cysts, or fibroids can develop in different parts of the uterus or ovaries and cause breakthrough bleeding.