Pretty common for my LOs after they have been bitten by mozzie. It's an allergy reaction to the mozzie bite. Will take some time to recover. The redness will spread then slowly fade away and replaced by dark pigmentation. The pigmentation will last for some time before it totally goes away. Apply some moisturiser and sun block lotion (before going out). Otherwise, leave it.
I went to the doctor today and was told it's blocked gland or something similar to acne on adult. Nothing to worry about, it will disappear :)