If you had unprotected sex and started taking a different brand of pills which led to midcycle bleeding, there is nothing to worry.
The bleeding you had today could be due to mid cycle hormonal
imbalances. If you started on a new pill (details not known) there is a possibility of such a thing happening in some women. It is known as Breakthrough bleeding
and will get normalised soon.
Hope this helps
Dr Anjana Rao