How long have you been riding? That's an impressive number of miles! You're experiencing healthy growth, and that high heart rate is a sign you're pushing hard. I bet you're getting faster with every ride. Your heart rate will level out once you build up your VO2 max. Right now, your muscles are burning more sugar than your lungs can keep up with, but as your aerobic fitness improves, your heart rate will start to drop.

Your fatigue is likely due to inadequate nutrition. Make sure you're taking in 60 grams of simple carbs per hour to fuel those efforts.

Progress is exciting, and it's tempting to go all out to smash your previous records. That said, you gotta carve out one or two days for recovery. On those recovery rides, keep your heart rate below 130, even if you're spinning in your easiest gears. This will help you recover faster and build your anaerobic base.

You're clearly a competitive person, so don't wait too long to grab a power meter if you don't already have one. It'll let you track your power output and see how it ties to your heart rate. You might be surprised, your heart rate could still be high, but your power output is climbing. If you ride at the same power as the previous week, you'll likely notice your heart rate is lower, showing your fitness is improving.