I had a strained hipflexor (at the left side) lasted about 4-5 months before it has completely healed. Mine seems not as severe as OP's though. I would feel the dull pain when I start the warm up jogging, then it disappeared after and would come back when I picked up the pace to say tempo pace. On one easy run, at about 10 miles, I started to feel the gluteus getting sore, then a few second later, my right foot just hurt really bad without any obvious reasons.
I went to have 3 ART (active release technique) sessions, they seemed to help a bit. One thing about the ART is that I would feel soreness at my core (especially buttock) even I rested for several days. After 3 ART sessions in 6 weeks, I still felt the hip pain. I started to do two things: first, some dynamic warm up before the run, like leg swing, lunge, it helped a bit; second, got a electrotheraphy device and applied it everyday, I believe this helped to heal my hip.