hi welcome to HCM.
-hi i had gone through your query and understand your concerns. i would come up with two possibilities.
1.the first one include;SCIATICA
-pressure on nerve,by tumor,or constipation
,or through injury ( lumbar spondylosis
due to degenerative changes in the lumbar spine
may be the cause in your case )
--over use of limbs walking
-rheumatism or gout
MRI scanning for lumbar spine may confirm the diagnosis
2.second possibility for blood in stool
is,PILES; proctoscopy examination may confirm the diagnosis
I hope this is helpful for you, thank you