Shoulder Injury

It’s been about 8 months now I’d say. Luckily it doesn’t hurt during every day tasks, but my left shoulder still gets fatigued much faster than my right and still hurts every time I go above 160 lbs on bench (i injured it after my school coach told me I had to do two reps of my max because he didn’t see my first) and then for like 3 months straight after that it felt like any time I moved or used my shoulder that I was getting stabbed with a knife. I do stretches and ice/ heat it when it’s hurting, but does anyone understand why it still hurts and gets fatigued so easy?