Please see a vet ideally within 24 hours if a guinea pig is blinking constantly and you also notice lots of clear tear fluid. In this case, it is a symptom of a potential injury (eye poke) or something stuck in the eye. Eye injuries can deteriorate very quickly but also heal much ore quickly and problem free if seen very promptly.
Eye cleaning fluid in guinea pigs is milky white; water tear fluid is always a sign of discomfort or irritation in the eye.
Occasional blinking is nothing to worry about (2-3 times a day). If in doubt, please see a vet with a piggy that is blinking a lot.