I started bleeding four days before my cycle calendar est. it has been two days and is now brown instead of red. implantation maybe? or an off cycle?

Hormones irregular: Something has changed your usual hormonal pattern so that you started this period early with less bleeding of only 2 days and now so slow it is brown. Pregnancy is a possibility but most likely an "off cycle". If you are having pelvic pain and tenderness, then infection is another possibility and if persists, see your physician.