Dude, Everytime I do legs I have the same exact problem! My lower right back almost into my hipbone throbs and is painful. The pain goes away after the gym so I just accept the fact that it will hurt when I'm doin legs. I
always squats, leg presses, lunges, and extensions for Quads and it has paid off big time. My legs have gotten so much bigger, I have gained more weight, and I believe doing heavy legs makes your whole body stronger. Stretch alot and Love the pain!
I used to make that my excuse for not working legs so hard but the truth is your not bodybuilding if your not hittin your legs hard. No excuses for legs just do it baby!