The brown blood is considered old blood which remained in the uterus or cervix for some time, while the red blood denotes fresh bleeding. With your history of irregular periods, this can be nothing of concern and seems to be part of your irregular period. Implantation bleeding is quite different (in amount and color) than the irregular period bleeding. See this link for implantation bleeding under the head, slight bleeding or cramping;
See this link for cause of brown blood;
Your follow up questions are welcome.