4 Days Late with VERY light brown spotting

Has this happened to anyone else?? I am 4 days late which never happens AND I am having extremely light brown mucus when I wipe. It has only happened twice in the last four days. I am 16DPO which is a little late for implantation bleeding. I took a test at 2 days late and it was a BFN, but what are your thoughts?? Should I test again? I have no other symptoms which is weird because my period cramps and breasts are usually really bad before my periods. The only thing I feel right now is a heavy and bloated lower abdomen! Thoughts??