BBT drop at 7dpo??

I've been tracking my bbt all month (my first month ever tracking) and I've noticed some cramping at 7dpo, about 10 days from when AF is supposed to start. I've very consistent with my cycle. Ovulated roughly around the 15th this month with opk's info. Af due 1/4. Is this normal? BD'd a lot around ovulation and used preseed for the first time this month. My temp was around 98 the last few days, but today is now around 96? Is that normal? I AM fighting a cold, but I'm not sure if that has anything to do with it.