bbt??? need some advice

So been tracking my bbt. It's been 4 days since my fertile window. My temp during consistently as been about a 97.4 I just tracked it today at 98.3 could I possibly be showing signs of being pregnant? I don't full understand the whole bbt that's why I ask. But today I also woke up after 8 hours of sleep and still felt exhausted and I've been in and out of sleep all day.