HELP! Ovulation Prediction Kit

i just started using an opk on August 6th. (cycle day 14 and supposedly the start of my fertile days) i have not gotten a positive LH surge since i started using them. ive taken all tests in the afternoon (between 2 and 6 pm) they all look the same. there is always a line, just not dark enough to be a positive. yesterday was supposed to be my ovulation day. negative opk result. am i not ovulating? did i somehow miss my lh surge? can i still ovulate? just got my mirena out about 3 months ago after 2 years. have had a normal period the exact days im supposed to (as glow says on my calender) just need help. thank you.