Do competitive runners absolutely live on Advil or what? I've somehow injured myself (again), and might end up taking a few days off, which professional athletes surely cannot afford.
And let's not even get started talking about the feet. A five-mile run is what? 10,000 steps? Which is what? 450 pounds of force absorbed into each shoe 5,000 times per workout? It's impressive how they can work through what must be virtually chronic pain.
You'll want to ask how old I am. Resist the urge. OK, fine. Let's just say that I'm almost 39 (in metric).
Sounds like you're suffering from overtraining syndrome. One of the sad facts of life is that most athletes, as they age, are not only slower but they need more rest and recovery than they did when they were younger. If you're training with the same intensity as you were when you were 10 years younger, you're probably overtraining. As for professional athletes, I would imagine that they can't afford not to take several days off when they're in pain. Otherwise, they risk serious injury and perhaps throwing an entire season away. For them (and us) cross-training is a good alternative to pounding out the miles on sore legs or feet (or hips or knees or ankles or...) and may in fact help reduce or prevent that soreness and pain in the first place!
If I am in pain, my body is issuing an emergency broadcast warning to me: DANGER, DANGER, TAKE THE DAY OFF! Unfortunately, pain is not a good early-warning signal. By the time I feel pain, I'm already well past the point of sensible training and I may be even on my way to injury. Of course, I'm speaking here as a layman and not as a physician, so I can only speak from my own experiences. Please do not take my experiences as medical advice.
The best early-warning indicator I know to determine whether on not I'm overtraining is to do an Orthostatic Heart Rate Test (don't worry - it's easier than it sounds) every morning without fail. If my heart rate is roughly the same for several days in a row and then suddenly it goes up by too many points one morning, say more than 15 to 20 beats per minute (bpm), that's a warning sign. It means that my body hasn't fully recovered and I should either do a gentle recovery workout or take the day off entirely. The best part about this technique is that it's easy (I take my pulse for 10 seconds before I get up, multiply by 6 to determine my bpm, then stand up and take my pulse again after 15 seconds, again multiply by 6 to determine my bpm, then subtract the first measurement from the second), it's completely reliable and – since most people already own a clock or watch with a second hand – requires no financial investment. What if you don't have a timepiece with a second hand? Simple. Take your pulse for a full minute. That's a well-invested minute that could literally save your legs and feet from injury.
Try that for the next few days and see if the pain you feel starts going away right about the time your heart rate goes back down to normal. But of course, don't listen to my layman advice. See a doctor instead.