I have a tight and sore hamstring on my left leg following a long walk, which had minor grade changes. sore on back left side of left leg.

Sore muscles: Sounds like your body wasn't used to the walking or grade. Minor soreness after exercise is normal. If a pain is severe or lasts longer than 5-7 days, call your doc. Otherwise, ice, rest, and consider light compression with an ACE wrap. Stretching exercises can also be helpful (like reaching to touch your toes), though take it easy for 2-3days