I started my last period 12/31 and it lasted until 1/4. I have a 27 day cycle and all my apps say I should ovulate on 1/13. I started taking OPK's yesterday. The one I took yesterday was pretty bold but not completely positive which I thought was weird since I was still 6 days away from ovulation. I took one today and the line is significantly lighter than yesterday's. Can OPK's fluctuate like that or did I ovulate super early and missed it ? Im really confused.