BBT is confusing

Victoria • Wife, mom of 1 little girl, due with baby boy March ‘19, dog mom of 2

So i started tracking my bbt honestly about halfway through my cycle. And it’s all confusing me. So far the last few days it’s been steady at 98.0 f. Well this morning 5dpo it was 98.7. Is it normal to have a random spike? I know it’s not much. But it’s been the same since i started tracking. Af not due for 7days.