OPKs for almost 3 weeks. Negatives!! Help!

Hi ladies!  Okay, so I've been ttc for about 3 months, stopped BCP in July, and just started using opk's this month.  My last two cycles have been about 28 days long and AF came as expected.  I've been taking opk's for almost 3 weeks and have yet to get a positive.  Glow keeps pushing back my period every time I enter a negative opk.  Originally, AF was supposed to arrive October 28th but now it's pushed back to November something.  I guess what I'm wondering is has anyone experienced this before?  I'm a little unsure as to what to do at this point.  Any advice/personal stories would be much appreciated!