some background: HS senior with PRs of 4:45 mile, 16:20 5k, and 1:18:30 HM
For the past few months my fitness has seemed to be off, but these past few weeks have gotten much worse as my heart seems to be getting higher on each run. It seemed to have started the last few weeks of track before the season got cancelled. I was only running 4:50-4:55 mile and 10:30 2 mile and was feeling abnormally out of breath/fatigued during these races as if there is something wrong with me. However, heart rate was still normal on easy runs during this time. The last week before everything got cancelled, I remember doing a sprint workout and getting abnormally out of breath on that and feeling a little dizzy/lightheaded after just doing a few sprints. That weekend was a meet and I ran another crappy 4:55; felt so flat immediately after the race started and just wanted to drop out the whole way. After that I decided to just take it easy for a while. However, starting on the next week the heart rate was suddenly 10bpm higher on a run at the same pace. For reference, usual easy runs at 7:30 pace the heart rate will start in the 120s and then will stay steady in the 130-140 range. But throughout the past three weeks my heart rate on runs is getting higher each day. Something also sounds and feels off in my breathing, I'm not gassed and dying but I feel "out of shape" and can tell something is just not right. The heart rate is now solidly 20+bpm higher at the same pace; it now starts out at 150bpm and gradually climbs and reaches 170bpm by the end of the run. Resting heart rate has gone up a lot also, it was 37bpm before all this started but now it has been 46-48bpm for two weeks (the first week it was increasing by 2bpm each day). I've been feeling really unhealthy recently, especially these past few days. I've been to a cardiologist before and do not have any heart problems, so that can't be a possible problem. I'm starting to think it could be low iron or an infection. Any thoughts would be appreciated.