Start keeping a food diary and track when symptoms happen as well. Write down everything you eat or drink, no matter how minor. I'm thinking it might possibly be an allergy or food sensitivity, maybe not Celiac, but along that line. Disorders like Celiac can cause full body symptoms, including dizziness, muscle spasms/cramping, back pain, night blindness, peripheral neuropathy (nerve damage), fatigue, weakness, dry skin, etc. It's definitely worth looking into.
Please keep us posted.