Does this sound like a hip flexor injury?

by Jeff
(Statesville, NC, US)

I'm 40, 6'2" and about 300lb and not extremely active. No specific "injury" occurred, but my left hip-actually the front/top of the thigh- feels like it needs to pop into place.

The main similarity to the hip flexor problems I've read about involve extreme pain trying to pull my left knee towards my chest (ie- to get dressed/undressed). There is almost no strength and I almost have to pick up my leg with my hands. I did see a doctor when the pin was more in the lateral region of the hip, and I had ultrasonic therapy that was only mildly helpful.

Does this sound like a hip flexor injury? and should I try the stretching and massaging?