Is it normal for eye to be still very sensitive to light 3 weeks after cararact operation?

Not unusual: The eye can reaon irritable for days to weeks, and even months following eye surgery, including cataract surgery. As long as the vision is good, and not worsening, you should be ok. If vision or symptoms worsen, additional eyedrops may be beneficial. Visit with your surgeon.

Inflammation?: Light sensitivity, aka photophobia, may be a subtle sign of persistent inflammation. You are encouraged to move up your next follow-up appointment, since the earlier inflammation is treated, the better the eye heals. Persistent inflammation may be sterile or a sign of post-operative infection so time is of the essence.