Question about faint line on opks?

This happend to me last month, by the time i used my OPK i got a dark line but it wasn't as dark as the test line, and then the next day it was even lighter, which means I had just missed my surge with the OPK. This is probably what happened to you too. Thankfully for me, me and my hubby were BDing every other day anyways, so I didn't miss it, we just didn't conceive last month. I hope your luck is better! And about the dip in your chart- it looks like you may have ovulated right on time. I would give it 3 more days of BBT's to confirm it though. If your temp keeps going up and stays up for 3 days then you can definitely confirm that you ovulated! I hope this helps, and good luck with TTC'ing!