howdy.

is it possible that it may be an ischial bursitis?

has this been discussed before, i only glanced over the postings. an unguided injection could have hit the bursa(e) and relieved inflammation for a period allowing your hamstrings etc to settle down and relax. the bursa is located under the proximal tendons of your hamstrings and adductor magnus and if inflamed is sore to sit on and can be sore to resisted testing of hams/magnus at times.

also have you had yur hip joints assessed fully?