Thanks Karen
I used the R.I.C.E technique (Rest, Ice, Compression, Elevation). I don't think I have been stretching properly and probably returned too early to playing. My Physio told me it was important to stretch and build up a comeback.
I done a series of tests with my physio. Stretching, pressure/compression on the muscle, strength tests and heat treatment which seems to bring out bruising in the muscle.
There's two ways I have been using to stretch. Firstly while standing I grab my right foot with my right hand and bend my leg to my buttocks. Secondly I kneel on one leg, keep my back straight and push my pelvis forward to include the hip flexor muscle. I used to have trouble with my hip flexor muscles when I was younger.
I haven't had any back pain with this injury. I guess the thing that is puzzling me the most is why I've still got tight muscles now even though I haven't run or pushed it hard for about 6 weeks.