My lo is 3 mths old today.. Recently these few days I notice that his eyes is kind of weird.. Both his eyes will move from side to side in a very very fast speed.. Is this normal?

Do his eyes kinda jiggle in a jerky movement or is he just looking around from left to right rapidly? If it is the former case, it could be Nystagmus (dancing eyes) - its not considered a serious condition, and accordingly mostly would go away after a while, but you should consult PD to be safe. https://en.wikipedia.org/wiki/Nystagmus