BBT and rice heating pad

Candi • Baby one born March 2016! Was TTC for 20 months. Scar on my tummy is from surgery I had as a baby. Now expecting baby 2 June 2019!
Hi! I've been having lower abdominal pain for the past few days and so I've used a rice heating pad at night. I'm wondering if it affects my bbt? It doesn't stay heated for longer than an hour.