Im sorry to hear about your symptoms.
Well from what you are describing , these symptoms are more consistent with diabetes than anything else. The frequent urination and dry mouth would also be accompanied by increased thirst as well. The tingling in the feet and calves as well as the fingers also point towards the development of possibly diabetic neuropathy. If this is the case, then getting a simple HbA1C level would be diagnostic. Fasting blood sugar should alo be done here as well.
now if we consider back pain and tingling and numbness in the calves as a separate issue then we can consider a problem with lower back as a possible cause. Compression of nerves in the lumbar spine due to disc degeneration or arthritis in the spine can cause these symptoms. this can also cause shooting or stabbing pain which can radiate into the legs. A simple clinical examination and xrays of the lower back would be helpful here. a MRI of the lower back however would be diagnostic. The treatment can be with painkillers, physiotherapy, steroid injections among other options.
Lastly a NCS/EMD test should also be done to rule out other possible causes of neuropathy in the limbs which can be vitamin B12 deficiency or even infections in some case. Weight loss would also be beneficial in all of these diseases.
i would suggest that you discuss these possibilities with your doctor.
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