Fitbit Resting heart rate rising each day - Opinions please

Nicole • Trying for baby #2 🍼 👶 INSTA @mummyto_babyperry

First day I bought the Fitbit I was 26/12 61 bpm which was the day I ovulated, then after a night of sleep it went to 57 bpm.

Since 29/12 it’s been going up 1 bpm every 2 days ish. Has anyone noticed this and ended up pregnant or does this normally happen before AF? Currently 4 days before AF.