A few thoughts I have about you and could be several possibilities.
Most likely it has to do with the last alcohol binge that you had a week ago. Some things to worry about are 1) pancreatis which is an inflammation of your pancreas which would cause stomach pain and radiate to the back.
2) Irritation to your stomach lining from alcohol and you could be at a risk of an ulcer
3) Gallstones- drinking can cause a risk of gallstones and the pain can spread to the upper back often accompanied by vomiting.
4) since you recently had what sounds to be like a viral
infection, this may very well be taking its course and resulting in the symptoms you are currently having.
5) constipation can also produce stomach pain if you have not had a bowel movement in several days.
I would recommend that you seek medical care and have proper blood work to rule out some of these possibilities. Until then keep yourself well hydrated and avoid any alcohol which may exacerbate your condition.
If you have any further questions let me know. Otherwise please click "accept" so that I can be compensated for my work. thank you