Brown spotting when AF due but not pregnant

I have an average of 25 day cycle and period is due today. I did a pregnancy test 5 days ago and negative. Did another yesterday (day before period due) and also negative. The last 2 days I have had dark brown spotting and some stringy stuff in the toilet after I wee. My period hasn't come today and now the spotting is gone too. Don't feel like I'm getting a period at all so wondering if that was my period. Had a miscarriage start of June but have had normal periods since then. Has anyone had anything similar to this? I'm not sure if I should get checked out by Doctor? I never miss a period. Thoughts ladies?