Positive 4 days in a row....?

These are my tests from the 11th through this morning. The lines are a little lighter in the picture because some are a few days old but all 4 tests showed a significantly darker test line within the first 6 minutes of testing. This has never happened and ive been using opks for awhile. The only thing different I am doing is i am on my second month of conceive easy. My fiancé and I are confused by this. I keep wondering if the tests are invalid? I have never had a positive for more than 24 hours. I know ive posted before about this so forgive me for being repetitive. Its just so abnormal for me. Anyone have the same thing happen?