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The first thing is that you need to see a rheumatologist to see if this is related to your dry eyes with a condition called Sjogren syndrome...leads to dry eyes and mouth. Artificial saliva will help with the sensation of dry mouth and make your mouth feel more comfortable.
Unfortunately this is not actually a problem with fluid intake, but more to do with saliva production. It will also put your teeth at increased risk of decay so you need to see a dentist.
The swollen sore tongue may possibly be a vitamin B12 deficiency so ask your doctor to check your vitamin B12 levels just to be on the safe side.