Hi,i started charting BBT this month only.i used OPK .i got a surge on day 18 but there was no temperature hike the following day.i continued using OPK.i got a surge again on day 20 but not on day 19.i dont understand whats happening .there is no hike in temperature and 2 surges on alternate days.Pls can anyone help in this matter.Thanks for your time.