Is lactac acid the cause of my leg's burning after working out?

its you working out its going to burn no pain no gain
try to eat bananas before and/or after (people say it helps)
and stretch so you dont pull a mucle
and who cares about latic acid acids happen when you work out because when you work out you are starving your mucles from air and ripping them so they could heal bigger.
i hope this helps