@nisa PT can help, but avoid the big chain BS. I have been dealing with this kind of pain for years, in the exact same area. I went the orthopedic route one year when i got tired of just dealing with the constant tightness and sometimes overwhelming annoying pain thinking it was a disc issue, but this was a wasted effort. The PT they had me do helped a little, but only to develop some of the stretch and strengthening routines i needed to focus on. Ultimately this route cost a lot of money. 1000 bucks for PT, 600 for MRI that found nothing, and a 'nerve' blocking technique they wanted me to do after the orthopedic doc couldn't figure out what it was and PT didnt really help to eliminate. Waste of time.
To me (or in my case) its a variety of elements that cause it. Two key things in my case are underdeveloped muscles, and incorrect posture from sitting all day for work. I am right handed so thus my right side during specific exercises like chest, back or bicep would over compensate for the left side being weaker depending on the type of equipment you might use. At least this is what I feel causes it the most. You really have to focus on form and starting with the basics, and using free weights as appose to smith machines. I have been working out for 10 plus years and only really started dealing with the pain you reference in the past 4 or so. It takes a lot of trying different exercise methods, stretching techniques, heat pad days, using a roller or lacrosse ball to roll out the tightness, and yoga techniques. For me to get it to a constant where it does not get tight and stay tight like you mentioned for weeks at a time. You really have to work at it. Personally I still don't have it all down, but I have gotten it to a point where its not noticeable at all at times for weeks. Everyone's body type is different, but imo I would try a more natural route before jumping on the orthopedic route.
Biggest thing that has helped me personally was first, starting by going to a good chiropractor. I started this a couple years ago and it helped to get my spine lined up to where it needs to be. This will at least ensure you bones/joints are lined up the way they need to be and not causing any additional nerve issues. Second and most important you need to find a good acupuncture place that does cupping or find, like others have mentioned, a sports medicine place that does cupping. The guy i got started me on the cupping and needling and it helps with the muscle tightness immensely. At least to the point where you can begin to rebuild. Building the muscle right is the biggest trick.
Again focus on the basics and form. Yoga is probably the easiest way to accomplish this. I myself need to get on joining a studio that specifically teaches different forms of yoga. Its the best way to ensure your core muscles are in the shape they should be. From there you can grow outwards. If you are doing stuff at home to start there is a ton of youtube videos. Yoga by Adriane is personal go to for me. Also youtube videos on form for working out as well. There are all sorts and you just have to play with it. The idea is to keep moving forward and dont give up.