if your gp wont refer you for an Wikipedia reference-linkmri or refer you to physio then go to someone different. its your health.

if you have been trying to strengthen your glutes with little success it may be that there are other issues indeed. for example there could be limited range at the hip, poor hip position, tight or overactive muscles like tensor fascia lata. it could also come from poor biomechanics further down the kinetic chain ie your feet. etc etc. its common enough to have hip problems after having a surgery like an acl as a lot of people tend to modify their gait to accomodate the pain in the post surgery period and this can lead to muscle imbalance. you say you had the symptoms before you tore your acl? in this case it may just have flared them up again.

i really would recommend seeing a decent physio who has experience in the lumbar spine/Wikipedia reference-linksij/hip. experience with acl rehab would help too.