Does the tightness come on suddenly?
I have never had sudden tightness but I get headaches a lot. Each and every time I fear it is a brain tumour but my anxiety is usually like a roller coaster; I can calm myself down but then it creeps back up.
As for your digestive and bowel movements, I can feel your pain; at the moment I am having weird pains; sometimes sharp, sometimes dull and acidy. None of us can diagnose you but all of these symptoms you are experiencing can be symptoms of anxiety.
Anxiety starts with your thoughts… if you can accept that it is anxiety, then your symptoms (if they are due to anxiety) will subside over time. It never works suddenly though (important to remember this); I went weeks without anxiety (on a conscious level) but my symptoms of anxiety persisted the whole way through and still do.
Check your neck muscles (at the back). At the moment, I have been getting slight headaches everyday. Yesterday morning, I felt my neck muscles and they ached as if they had been put under strain for hours on end. They are still aching now and will do for another 2 days maybe. The pain goes right the way up to the back of my head from my traps.
Also, how old are you? If you get sudden severe tightness in your head (and I mean excruciating pain to the point where you wouldn't have the patience to create a topic on here), that would be a cause for concern immediately. But if it doesn't impair your daily activities, maybe go see a doctor to make sure it is not anything alarming but other than that, you can safely expect it to be anxiety/stress related.
It's the same with your digestive/bowel problems; persistent, or sudden severe pain, blood or severe constipation/watery stools that impairs your daily activities would be a cause for concern; check with a doc but if all is clear, then you can safely conclude that it is more likely anxiety/stress related.
But none of us here can properly diagnose you, obviously. So don't take our word alone.