My back pain got pretty serious for a few days.
Right side hip flexor from the lumbar, around & over my hip.
On Monday, I didn't have a foam roller or lacrosse ball to work on my back so I improvised and used a small medicine ball and a aerobic step. I put my shoulders on the step and laid on the ball and, while experiencing ridiculous pain, rolled my tightened back/hip area over the ball several times. For about half an hour.
Then I did all of the yoga positions from this travel stretching workout from Greatist.com, which nearly all focused on my back and hip flexor.
This hurt like hell, but it did the trick.
On Thursday, I repeated the yoga and did several other hip flexor stretches.