Had lasik 5 months before. Now when I wash my eye with water, eyes turns red from corner and feel temporary mild pain in corner and on upper lid. Why?

Unsure. Not a typical collection of symptoms, . However, your symptoms seem to be associated with irritation to the surface. Your eyes may be dry. Please communicate with your doctor to make sure your healing is progressing as expected. Only they can identify the problem and treat it.
Probably not related. Hard to know the cause without an examination. Could be something as simple as an in-turned lash or an early stye. I doubt it's related to your lasik sugery.
Need eye exam. It is impossible to diagnose conditions such as what you're describing without an eye exam please call your ophthalmologist.