I am so sorry to hear about your increasing undiagnosed pain. We know hoe very frustrating that can be... my heart goes out to you.
It's difficult to guess what may be going on with you. It major stomach conditions have been ruled out then you need to consider that this is referred pain. Meaning that it is felt in one area but originating in another.
You're fairly young to have DDD (Degenerative Disc Disease) but it's not an impossibility. There are other spinal issues that may be the source of your pain. An MRI would rule out any spinal structure issues.
The pressure in your head may be due to the fact that you are "anxious." I assume you have had your Blood Pressure taken and it is not due to hypertension.... but that can cause "pressure" in your head and should be considered. Anxiety can cause an elevation in your B/P which would also explain the pressure you are experiencing.
Upper back pain can also be present in large busted women. An employee (young) of mine had extreme upper back pain that also caused some abdominal pain. She sought the opinions of some of the best physicians in our area. MRIs and all other testing came back negative. One astute physician finally suggested that her pain was due to her large bust and suggested a breast reduction. You guessed it, the breast reduction surgery eliminated her back pain.
I cannot guess what the cause of your SX may be. I told you about the above situation to say that there are many reasons, sometimes elusive ones that can cause pain. It may take a little thinking outside the box to get to the source of your pain. Don't be discouraged, be assertive and demand answers.
If you are not satisfied with the physicians you have consulted... get a second or even a third opinion. It can't hurt. This is your body and no one knows it better then you do.
I hope you will keep in touch and let us know how you are doing. I will look forward to hearing from you soon.