What is the reason why freckles or blemishes appear even if I apply sunscreen every day?

I honestly tend to apply sunscreen almost every day out of habit. Even on days I don't go out, I make sure to apply it in the morning as a basic necessity, and I try to reapply it in the summer. However, strangely enough, recently I've started seeing one or two faint spots of pigmentation on my cheeks.

At first, I thought it was just a temporary mark, but it seems to become more noticeable every time I look in the mirror, so it's stressing me out for no reason. I'm not exactly sure if it's melasma or blemishes, but my skin tone feels less even than before.

I'm not sure if it's because I didn't apply enough sunscreen or if I didn't reapply it frequently enough. Or could pigmentation be caused by hormones or lifestyle habits, rather than just UV rays?

I'm also wondering if this kind of pigmentation can be managed with home care. For those of you who have tried Vitamin C, whitening ampoules, or toning treatments, did you see any results? Once concerns about pigmentation start, they become increasingly bothersome, so I want to manage it proactively.