I drink approx 3L water and work but still get really thirsty in the evening, feels like my throat 'sticks together'. Why would this be?

Can't be something . else cooking. This needs to be checked on whether it's iatrogenic, meaning medication induced, or whether it's something different altogether that could be related to electrolytes and glucose, insulin regulation, or neither. Have your doctor look at this with you, and run more tests. .