Higher than Normal HR

Hi! So I have slowly eased back into running after coming from an injury. I ran a 5k race at a pace of 9:43/mi and my average heart rate was 165mph. I got sick after the race and took a break from running. Two weeks later I ran 5.0 miles at a pace of 12:22/mi and my average heart rate was 155mph. I am a bit concerned as I ran much slower yet I struggle to get my overall heart rate slower. Specially my HR spiked up the first mile and then for the last two? Any thoughts/ suggestions on how to lower my overall heart rate?