Aleviating Back Pain from studying

Hi everyone, I’m new to the forum and this is my first post:

I’m currently studying for a big standardized test 8ish hours a day. This requires long hours writing at a desk (I’ve also tried on the floor, stretching my back the opposite direction) and almost constant movement of my writing arm. After a few days of this, I have developed a very painful and unrelenting “knot” under my left shouldblade (I’m left handed).

I do yoga every morning (Beginner level) and have tried many stretches to work this out/alleviate the pain, but to no avail. I’m wondering any good techniques that can fix this problem. I will be studying for this almost every day for many weeks, and do not have the time to be focusing on the pain, nor time to take off due to the pain.

Thanks,
Simgar