What to do about a sore part of my back?

Last summer I went for my BMQ training. (Basic Military Qualification) For the last ruck sack march that we did, it was the 13k march that took us about 2.5 hours. The ruck sack, I believe was weighing somewhere around 50 pounds. During the last half hour, my upper right back near my shoulder blade started to cramp. I think it cramped the entire way back to the barracks, and the weight of my ruck sack made it worse, but it also was easier to ignore the pain at the time because of that weight.

It’s been a year now, and it never really hurt after that course, but now I’m feeling soreness when I awake in the morning, and in random parts of the day. If I look all the way to my right as far as I can, that part of my back that had cramped up during the last ruck sack march feels strained. Or when I do a right shoulder check while driving and changing lanes, that part of my back aches.. (>__<)

What shall I do in terms of ridding myself of this sore/ achy/ straining feeling?

I’m not sure if the opportunity cost of going to the doctors is worth it… unless you can persuade me that I may suffer serious permanent damage.. it’s easy to get me paranoid

Any suggestions? Know of any back exercises to strengthen my back?

(If this helps, I am a 19 year old female.)