What Causes Severe And Alternating Pain Between Legs?

Hii



I am a 26 yrs old female.From last one month i am having severe pain in legs (not at any particular point but completely)And the strange point is when one leg stops paining other one start paining more severly at the same time



I consulted one phsiotherpist who told me its nerve root irritation in back but i dnt have any pain in back



Please advise