From what I know...a + result from an OPK means that you most likely will ovulate within the next 12-48 hours. Sometimes people see a pre-O dip in temps right before ovulation. It is possible to have a + OPK result (showing the leutinizing hormone at its peak) and then not O, but I think that's not very common, so let's just assume that's not what happened for you.
I'll tell you this...on my current cycle, I got a + OPK result, another + the very next day, then a -...then I stopped testing. Fertility Friend states that I didn't O until about 4 days after the first + result, so I guess those OPK's can be used as guides, but they can't be entirely relied upon.
My hunch is that you're very close to your O time...so keep BD'ing until you see significantly higher and sustained temps!
~Sandy/DD born via emergency C at 35 wks/1 day June '03 due to Severe PE/class III HELLP
Risk factors: HBP/asthma/high cholesterol
currently trying to catch an egg...