Hello, I am having my mirena removed on Friday and have started OPK testing to be aware of my cycle and when I should start my period after removal. I ahve had light periods on the mirena for the past few months lasting only a day or two. I have gotten 4 days of positive OPK with the equate (Walmart) brand. And today I decided to try a first response and it was negative. The test line was actually barely there, even though the equate brand was positive earlier today. My question is should I trust the first response since it is the more expensive and sensitive kind? So they say at least