Dried mouth, back pain and dry eyes. what could this indicate?

See eye doc: See your primary doc and make sure you don't have a viral syndrome or autoimmune problem where your immune system is attacking yourself. Then see eye doctor to llok for sjogrens syndrome.

Medications?: Any medication with "anti-cholinergic" activity could create this combination of dryness, though i think the back pain may be unrelated. Antihistamines have some anti-cholinergic activity too.