Nosedive? ☹️

So if my temperature 🤒 took a nosedive 4 days after ovulation, does that mean I'm out this month? I've read that this body temp thing shouldn't be used, because in most women there's no significant temperature change. Is this true? Not sure what to believe. How much significance do you ladies put on the temp thing?? Also, if you get up and move around a bit, surely that makes a difference. Should I be reaching over and taking my temp in bed, before I even open my eyes??!