New to BBT

So I took my temp vaginaly at 4:30am twice it came up at 98.0 . . now a little while ago I took it just for the heck of it and it went down to 97.7 BUT I had already been up to pee and feed my cat and dog so should I not even count that as accurate ? .. My period is due the 26th .. I heard anything at 98.0 and up is a good sign for possible pregnancy !