Hello Doctor, I suddenly had a a severe lower baack pain 2 n a half weeks back.But now the pain has reduced but there is tighness in my thigh and littlte pinching pain near my tailbone(to the right and sometime to the left)...and just around my bum area.I am not able to sit for long though...and if i stand my legs feels little weak. I had taken physiotherapy for 9 days....and had consulted a doctor who said its something in the SI joint .IN MRI SI joint is normal.So is it just a muscle sprain?Nerve problem?I am 28 year old femaile...and i have a sitting job but i am active as i go for joggin walking swimming and occassional horse riding(just trottingt only)