You need to go see someone who is qualified.
Getting stretched out and all of that is good, but, when you start the movement pattern and start having the same issue again it usually indicates an underlying issue. It may be an injury or strain, it may be caused by (and usually pretty easily fixed) an imbalance or movement issue that has developed over time.
No offense intended but a trainer at a JC is probably only going to be so good. I know a kid (who was drafted as a LHP), then had to have shoulder surgery, who is at a D1 currently ranked in the top 30. What does his rehab look like? Well, he is working with a kid who is a senior in college and is a part of the training programming at the college. In other words, someone who doesn't know jack. To me it is insane for a kid with draft position and money on the line (not to mention long term health) to work with someone who is still trying to get his degree. My son played six months with a missed diagnosed back problem....the trainer at the school he was at was young, inexperienced and made a lot of assumptions....in other words, didn't know what he was doing.
No diagnosis. So, the problem persisted and he was cut because his performance was impacted.
The lesson is, you need to take care of yourself and make sure your well being is being addressed, because chances are, no one else will. Even at the JC level baseball is a business. It usually is not treated that way by the kids who are playing it. I cannot say this enough....understand that your health is not your coaches concern. He may be a nice guy and he may care....he may very not care at all either. But, his job is to win games (and keep kids that pay tuition) and thats it. This is why over recruiting at nearly every level of college baseball is such a problem. Speaking in general terms the coach cares about winning, he sees players as names on a depth chart and little else. He does not care (at least that should be the assumption).
You may have to spend some money out of your own pocket or mom or dads pocket but you should go see a physical therapist or a sports medicine specialist that is qualified. If I go to a guy who works out of his garage to fix my car and a week later it is having the same issue I would never go back. There is a reason a good, honest, qualified mechanic costs money, they are worth it.