You would count the day when you actually start bleeding, not the days you spot. If you have a 28 day cycle, you might want to start using the ovulation test on day 13. The first day you bleed is considered CD1, so start testing on CD13 until you get a positive on the test, its best to take the test sometime after 10am, dont use first mourning urine, and take the test each day same time. Answer ovulation test(20day supply about 20 bucks) works pretty well. But you may want to monitor your cervical mucus and take your temps because it could be a possiblity you are not ovulatating
I just bought an OPK and I thought it said to start testing on CD 7 or 8? I have a 28 day cycle and if I tested on CD13, I would have missed my ovulation. Just thought I would throw that out there. You might want to start testing earlier to insure you aren't missing you're ovulation date, then when you have a pretty firm grasp of it, you could narrow you're testing days down?