I don’t have an answer for you. Yet. I’m trying to figure it out for me too. Not so much the speed training you’re doing—I’m not doing anything so formal—but the workouts and practice I am doing, are getting to be murder on my hip joints. Especially the left one. And I’m about a half decade or so younger than you.
I’ve been doing hip flexor stretches after warming up, and adding the rest of the lower body stretches I did in H.S. Track too, but not getting much joy. Losing weight is helping, a tad. And I have a theragun sort of thing I’ve been using now too. But this and ibuprofen just makes it sort of tolerable. Not great.
Is the pain and weariness constant? Or is it a post-workout and next day phenomenon? After two weeks, I’d think your body would start to get used to that exercise, there, and at that intensity.
Bring it up with your general practicioner? If only because it may be exacerbated by something medical, and not merely the exercise stress.