Shoulder pain when FH looping underspin

The 3 things that I focused on in yesterday's practice was the placement of my left foot to get in good position for the ball, rotation of my torso as a unit including elbow + upper arm, and ending my follow through up above my left eyebrow.

Of all these things, I'm finding the most difficulty with my end position still going across my body mostly due to habit.

The one thing I did notice though, is it seems to strain my scapula more than my previous stroke so I probably just have overall scapular weakness and may need to get some light weights and restart my rehab back from all those years ago. 

Perhaps right now my should will not sustain my motion but not to worry, I rarely go for loop kills and take care to miss the ball rather than reach or hurt myself. I'm too TT-crazy to step away from the table and rest, sorry guys!

Also, as much as I would like, I can't afford the only decent coach in the area because he's $50/hr. The rest of the coaches offering lessons don't have the oratory skills or even temperament to properly put into words what they are doing even though they are solid players in their own right. I'm sure we're all familiar with the adage of great players not necessarily being great coaches.

Thanks guys!