Slight increase in my resting heart rate?

I have a fitbit HR. Normally my resting heart rate is around 50-52, but about mid month, around my fertile week (did not confirm with opk) it gradually started to increase to about 60, which is what it's at now. I'm not anymore stressed than normal (in fact less so because I'm a teacher on summer break). I haven't been able to find much online. Has this happened to anyone else? Bfp or bfn? I even went back to last month and it didn't show an increase around the same time.