I've found that cm isn't a reliable indication of fertility in itself. Have you checked your cervix or do you know how? Simply use your middle finger - because it is the longest - to try to find it. It feels like a little ball. Once you find it try to determine if it is open or closed. If it is open in addition to the ewcm you could be getting close to O. If it is not open, you may still be a few days away yet. Hope this helps! I'm going through the same thing right now. My baby is 4 months old and I'm trying to determine where I'm at. My cycles have returned to normal, the typical 28 days between bleeds, but I don't believe I have O'd yet because my opk lines have been so light.
P.S. as a tip you'd probably get more answers if you asked this in the TTC thread... those girls over there are experts at cm lol.