u/738arm29

I’ve been running for about 6 months now and about 4 months ago I got a garmin to track everything. I’m 28 y/o 6’1 and 188lbs. I’ve always been into sports and stay active but still new to running. I’ve worked my way up to about 20+ miles a week and constantly running 11-12 min miles is killing me. Trying to keep my hr under 155 bpm it so challenging and although I’m getting better at it I’m not seeing much progress at all. I just started implementing intervals and I’m hoping that with help but ideally I’ve been hoping to see my hr start to drop at the same pace but it hasn’t done anything. I’ll I’ve managed to accomplish is getting slower. Any advice?