Do you count your own resting pulse or did you get it from the heart monitor (and are you counting it before or after your run)? 120BPM is a bit high for resting. When I didn't work out back in college mine was 80-90BPM; in the last three years it's come down to 60BPM or less. You've been running 8-10k since last fall so your resting HR should be much lower.
Your heart monitor may not be properly calibrated. Check your input settings again, and if that doesn't work see if you can borrow another heart monitor and see if you get the same reading.
1) eat real food - more vegetables, moderate meat, moderate fruits, less grains, less sugar, less vegetable oils.
2) exercise - moderate intensity cardio, sprinting, heavy lifting, dedicated stretching and mobility.
3) live - relax, de-stress, meditate.
Disclaimer: I'm not professionally qualified to make any formal recommendations. I've just done my homework and I'm my own guinea pig. All of my data, unless otherwise cited, comes from a sample size of n=1 (me).