My husb and me are planning for a baby. We used OPK this month to check when exactly i ovulate. Length of my menstrual cycle is usually 27/28 days. I constantly checked for ovulation starting from day 9. Till day 12 it showed a negative result and on day 13 (yesterday) it showed a positive. I checked again today (i.e day 14) and it showed me a negative result. Does that mean I ovulated on day 13? Is it normal for OPK to show just 1 positive result? Should we have sex today as its a negative?