Seeing what you do for a living, the pain could definitely be from that. Or not. You're young for it to be that, but all that bending could be part of it. The backpack could be pressing on nerves in the shoulder, which can spread pain down. This is actually common and it happened to me when I was in college, saw a doc and she must have seen a lot of cases like it and told me about heavy backpacks. Anxiety pretty much works like this: you get anxious thoughts, even though many times we don't at the time notice we're having them, and when they get strong enough we can suffer a lot of physical problems, especially when sleep is disturbed by it. But different people get really different symptoms and some don't get many physiological symptoms at all, it's almost all mental. A lot depend on your life -- I got my chronic anxiety as opposed to episodic when I was already a heavy exerciser and daily meditater, so I think those things protected me from the physiological things my sister suffered from when she got the same problem. It's always difficult to attribute stuff to anxiety, because anxiety sufferers get all the same things that others get but often our docs find it easy to blame it on anxiety when the basic tests come up negative. Sometimes you just have to be persistent and see the right specialist if you're at a point where your anxiety has gotten better and therefore you don't think it's that. There's no way for anyone to know for certain, so do look at your life and how you've been thinking lately to see if maybe there's a trigger you might be missing, but also trust your instincts and if you think it's physiological persist on finding the problem. The one issue that's really out there is needing to go to the bathroom every time you drink water. Really anxious people do need to go more often than others, but that's a lot and might be a signal of something. Good luck.
People do tend to have GI distress when highly stressed or suffering anxiety disorder. IBS or irritable bowel syndrome is tightly correlated to stress and anxiety, for example. Your work is physically demanding. I know that after a car accident more than a couple of decades ago, I have an injury that flares from whiplash. I get headaches when either stressed or if I aggravate it from activity. Pulling weeds, for example, can result in body aches and headache that makes me feel ill (weird. And no, I don't really use it as an excuse not to do the household chores, ha ha). Stretching helps. Do you take time to stretch?
As to a doctor wanting it to be quick, I've thought about these things. So many of us feel like the doctor is running the show but really . . . we are their customers. We pay to see them, we drive to their office, we should be the ones that are in charge. But it is that authority figure thing that many have in which they are intimidating and we view them as the ones with the power. Really, you are the consumer there and have every right to sit and ask question after question after question if you need more clarification! Sometimes it helps to take someone with you to the appointment. They can write things down, ask something you forgot to ask if you make a list ahead of time and back you up if you still aren't satisfied and need a bit more of said doctors time talking about things for you.
I do agree that when we start to have an issue after doing something new (vitamins), stopping them to see if it goes away may provide relief. So, that is worth trying in my opinion. In general though, vitamins tend to eventually after taking them for a while help me with energy. You should like this has been the opposite but everyone is different.
You can absolutely get physical symptoms from anxiety and stress. The big complaint of kids with anxiety that is diagnosed later is stomach aches. Next thing you hear is headaches. I'm wondering if a few things you add in on your own could help at all like doing a bit of yoga, meditation, practicing breathing techniques, stretching routines. You get a lot of exercise from your job but a walk or something of that nature, or lateral movement is also quite calming to the nervous system.
What would you say is your biggest concern of your symptoms currently?