Go to a foot doctor, you may need arch support. My brother who in not a UPSer, he is much smarter then me had this issue.
They fitted him for arch support and he has not had any pain for years now. But until he got the arch support he had pain up his legs into his knees and lower back.
He had days he could not walk without looking like he was 90 years old, he was in his mid 20's. Today he has no pain, walks fine, runs.
If you have bad arches you are in trouble in this job unless you get help, medical science is a good thing you have health care use it.