Lower right back pain that radiates to lower right pelvic area for months. possibly ibs?

I have had this since March 2011. Bad pain in my right lower back.. right hip.. right lower pelvic area.. into the top of my crotch and down by where my crotch and leg meet. I am a 21 year old female. Went to the doctors.. he suggested anxiety since I have had anxiety and panic attacks since 2005. I did a urine test that came back fine, had an renal and abdominal ultrasound which came back fine. I was thinking IBS since im very irregular... the pain is odd though.. sometimes it feels like i have a rock in the right side of my abdomen, or sometimes it hurts to move like its a muscle.. or sometimes its a stabbing pain for 3-4 minutes in the lower pelvic area and then it goes away... and then sometimes it shoots down to my leg. Very odd. My doc said to take probiotics.. so im taking a probiotic plus fiber.. and the pain seems to almost disappear when im on it, but i ran out for a week and the horrible pain came back.. finally just got some more and it took 4-5 days of taking it and it is almost completely gone.. seems odd?? i just dont want it to be something serious but my doctor doesnt seem to be worried.. wondering if this is ibs symptoms?