Sorry man, just saw this.
First, go see a medical professional who can accurately diagnose you in person; none of us can really do so over the Internet.
Ok, so with that said my guess is that you are experiencing impingement due to improper scapular/shoulder positioning or weak/unstable shoulder stabilizers. All of those exercises that you mentioned can be good, but it's easy to compensate or perform them less than optimally.
Look on youtube for an exercise called "Wall Extensions" which is posted by gymnasticbodies.com. Form notes to keep in mind:
1) the head, lower, and upper back must stay in contact with the wall throughout the entire exercise
2) while the true exercise is to be performed sitting on the floor with legs straight out in front of you, if it's impossible to even get into the starting position you can regress the exercise by standing against the wall instead (with the feet out in front at an angle
3) you must keep the outsides of the elbows against the wall and at least the knuckles as well (though in actuality the backs of the hands/wrists should be in contact to consider this exercise truly mastered
By using the wall as a tactile cue it will force you to perform the external rotation correctly/strictly. Let me know how that goes.