Talk to General Physician on Dehydration

Height 5 ft 1 inch. 56 kg weight. ✔️Sudden dehydration problem from 5 years. ✔️Severe headache to the extent vision gets blurry sometimes. ✔️Body heats up and starts sweating ✔️Frequent urination ✔️Sometimes irritation while urinating ✔️Gets better when I keep drinking water but get dehydrated so quickly even with 8 hour sleep gap. ✔️gets severe if because of work/travel I'm unable to drink a liter in about 3-4 hours. Tests done: ❌ BP and Sugar normal ❌ Thyroid hormonal test is clear ❌ Liver functioning test is clear ❌ Do not have any stomach issue ❌ No bad eating habits or smoking etc ❌ Eat normal salt in food. What could be actual reason? What tests medications would you recommend?