My resting heart rate has averaged in the 40's consistently over the last two months, and in that time I have greatly increased my activity. Below are my metrics over the last five months with June and July being very active for me.
March: 54
April: 55
May: 59
June: 51
July: 46
Some days, like today, I get a resting heart rate average of 42. All this to say I've been getting consistently lower readings since my activity has increased, which is typical. If you aren't active and getting readings below 50bpm, then I'd see a doctor.