Lh surge after bbt rise?

Anyone else experience this? My chart shows a rise in bbt (to a steady .8 degrees higher) 3 days in a row, but opk tests were neg on the first 2 days (as well as the 3 days prior, so neg opk for 5 consecutive days total)...opk positive on 3rd day of the rise (6th day in a row I had tested).  So which do I believe?  The bbt or the opk??  As I understood it, I should ovulate *before* a rise in bbt (which would be quite early in my cycle), but *after* an lh surge.