your body has been through alot, the radiation has made every muscle and tissues in your pelvis very tight ang fragile so soreness and pulling and aches are to be expected. The good news is that as a mail carrier you are very active and this is good because as time passes everything will stay nice and limble. Do make sure you stretch in the morning and before bed as this will help tremendously. It is important to keep your sciatic stretched out. Although these pains will bother you for awhile after treatment in a few months you will not even notice as much.
If you are finding that the pain is getting too much then speak to your GP about pills for nerve damage or physical therapy to help. Do make sure you invest in some orthotic shoe insoles as they will help.
Between the operation, radiation and chemo your body needs time to heal and it will take up to a year to recover.
It does get easier as time passes. I'm almost 10 months post treatment and some things have improved greatly I still get sore feet and achy hips once in awhile.