Strong pain in the legs


At first i am really happy i found this beautiful forum ! :slight_smile:
I want some help please in my first thread!
I am 25 years old and i started yoga (mainly strech yoga and body balance) in September 2016 until Juny 2017, then i stopped for 2 months and from September of 2017 till now i am doing body balance 2-3 times a week and more rarely yoga.
Just really recently i realized that my frexibility have increased importantly, even last year did not! But some days now i have really strong pain in the legs. In Sunday the pain was only in my pelvis but it was enough strong, then Monday, Tuesday, Wednesday was from my hips tο the middle of the thigh and yesterday was from the middle of the thigh to down and it was a really strong pain! I even took a painkiller 2 nights because i could not sleep from the pain.
I eat as before i am not overdoing with exersicing, i had a flu or a cold for 2-3 days but i don’t think it was to do with this because i don’t have pain at all in the rest of my body plus i am fine now and the pain still exist.
Maybe it has to do with flexibility?
Because as a child i was not doing yoga or something else that is increasing flexibility.