re: patient no.1 22 yo soccer player.... insidious onset or sudden from an event? have you checked adductor tendons and tested for osteitis pubis or derivatives thereof? is hip quadrant test negative (full compression + flexion + adduction through ROM) which will test the integrity of the joint itself. What is player's core strength like (ie. is she reliant on iliopsoas and power muscles for pelvic girdle stability rather than TA and core and especially glut med.)? is the pelvic list/tilt/rotation equal on step length between the legs. also what would you expect to achieve with interferential other than masking pain? one other thing, clear the knee as anterior hip pain can be and up-referral from the knee, and ensure ITB/TFL is not contributing to poor biomechanics.

Re: Case 2: a generalised inflammatory condition or acute infection such as strep throat will increase global inflammatory markers and inhibit healing tissues. once the throat infection is sorted the knee should come good again.

re: case 3: is the pain the same as shingles pain and in the same location? this can be ongoing for many years post acute infection of shingles. if not shingles pain then do full Lx assessment as you would for a degenerated disc/ OA spine etc. as the LBP may not necessarily be directly related to the shingles. full list of aggs/eases, treatment to date, pain type: intensity, duration , severity, irritablilty, physical Ax. If you're really stuck, diagnose by elimination: define your list of potential issues in order of priority then treat one thing only per session with only one modality/method and reassess.

good luck