Can anyone give me a clue what might be up with me?

[Locatistar]

For the past two weeks I've had
Diarrhea (ranging from pure water to loose stools 6+ times a day)
Constant nausea
Lower back pain
Pain between my shoulder blades
Difficulty swallowing (like food won't go down.) also I am choking a lot more than usual because things have gone down the wrong pipe
A feeling that the valve between my stomach and œsophagus is open (just a feeling.)

Any thoughts?

You need to see a doctor rather than ask unqualified internet people.

for you. It could be a number of things. Definitely see your GP. Hope you are feeling better soon.

Sorry you are feeling ill. I've had similar symptoms and am being tested for a variety of things ATM, some straightforward, some a bit scarier. You need to get yourself to a doc who will most likely schedule blood tests, stool sample, ultrasound, endoscopy/ colonoscopy type tests. So get thee to a gp!! Good luck

Two weeks of that? You definitely need to see a Dr. Meanwhile make sure you stay hydrated and maybe add sugar and salt to water so you are properly re-hydrated. This is from NHS direct -
Oral rehydration solutions.
When you're dehydrated, you lose sugar and salts, as well as water. Drinking a rehydration solution will enable you to re-establish the right balance of body fluids. The solution should contain a mixture of potassium and sodium salts, as well as glucose or starch.
There are several different rehydration products available over the counter from pharmacies or on prescription from your GP, including solutions that are suitable for infants and children.
Ask your GP or pharmacist for advice about the most suitable rehydration solution...