You usually don't O on the day of the + OPK. You should O within about 36 hours
after. And then your temp finally should go up after that.
So if you got a + yesterday, and maybe are Oing today, your temp should start rising tomorrow. Some people do have dips on the day they O. Or you might O tomorrow (that would still be within the right time after the + OPK) and then your temp would go up the next day.
Get to BDing! Be sure to get in today at least.