Your description sounds similar to my own experience. I won't attempt to suggest a "diagnosis" because there are too many possibilities & only an OS with diagnostic tools can do that, but here is my experience.
I am a whitewater boater, and (partly due to a particular technique common at that time) suffered with impingement and rotator cuff tears and eventually dislocations. At the time arthroscopy didn't exist, so the first two rotator cuff tears were open surgery, pretty standard. Eventually I dislocated again, this time a "Statue of Liberty" dislocation similar to what you describe, including the excruciating pain. The pain was so severe I could not stand to lie still: instead choosing to walk out rather than wait for the EMT's, with 2 friends holding my arm vertical! (This probably contributed to nerve damage; initially I was unable to move the arm, and took months to fully regain sensation. I still have a slight "prickly" sensation in the 4th & 5th fingers due to permanent damage to the ulnar nerve..) After this I was a chronic dislocater -- it would pop out while swimming, reaching under lab equipment, etc etc, but I could always coax it back in by lying on a table & letting it dangle. Eventually this got old, and I had a Bankart procedure. It was open surgery, labral tear more complicated than the routine rotator cuff tear. (You can search & find out a lot about it so I won't try to explain.) The OS was the team OS for a major league pitching staff and also Pam Shriver, so he was pretty good! After that I never had problems with routine dislocation; altho I was nervous for a long time, eventually I just routinely "forgot" about it. I have had an impingement-type tear since, which was repaired arthrscopically with an excellent outcome.
As Dr. Gross said you need a good evaluation, and I'd add, be sure you get a good sports-med specialist with lots of shoulder experience. Since this is an on-going problem that you have had for a while, I would also suggest educating yourself a little so that you can ask good questions and be an informed patient, because I'm a firm believer that that understanding will help you with the PT routine during recovery . Here is a non-physician guess based solely on my experience: you may (as I did) have two different types of injuries: a labrum-type injury of some sort which was the major event you describe, and also possibly some quite different damage to one or more cuff tendons.
Finally, of course you know that absolute compliance & concentration on the post-op therapy is a must for optimum outcome. (And don't make sudden increases in strength routines. )
Good luck, and I strongly urge that you look around diligently for the right OS & get it evaluated ASAP.
It sounds as if your initial surgery was unsuccessful, and that you are now experiencing recurrent dislocations of your shoulder. Its impossible to say for certain, but most likely, you will require revision shoulder surgery. That is, the original surery will need to be redone.
I suggest evaluation by an orthopedic shoulder specialist.