Resting heart rate

My resting heart rate is usually around 72-75.

But for the past 2 weeks it’s jumped to 79-81.

I’m not more stressed than normal, I’m not sick, I haven’t gained weight or changed my diet.

The only thing that’s changed in the past few weeks is I have started taking prenatal vitamins. (Not pregnant yet)

Why would my resting heart rate go up so high?