Hip Flexor??

I pulled my hip flexor a couple of months back. It healed and all was good. Figure it was caused by overstriding. Backed down on my stride and everything had been well.  Now I am training to walk a half marathon and notice at 2.5-3 mile mark, I have the same pain in the same area. If I try to walk through it, then I get an aching in the upper pelvic area that wraps around to the back. Also sometimes down the IT band area.  Any idea for stretches or exercises to try to strengthen this area. I do stretches for the hip flexors before, during, and after my walks. Running out of ideas besides to start physical therapy which is a little bit expensive right now even with insurance. Any help is appreciated.

I had band surgery on Jan '08 with RNY Nov '11.

I like the kneeling hip flexor stretch

Kneel down on one knee. Slowly press your hips forward until you feel a light stretch in the front of your thigh. Hold for 30 seconds, then alternate legs If more stretch is needed, bend your back knee toward your rear end.