Yes that can be the reason that it is weird. I got a new one last week Off Ebay with 20 IC Ovulation strips ( or HPT'S) and the thermometer for $11.99 shipping and all. I got my old one from Walmart close to the Hpt's and Ovulation test.
You have had a lot of W CM all cycle and after O it usually is not W you may want to see f it has a white color in it then it would be C CM because W CM means Fertile and that after O will sometimes throw FF off just something I had a problem with when I 1st started charting.
If you have any questions please feel free to ask