Gums look white on both sides

My son is 4months old and just recently, he cant finish his milky unless he's really hungry. I tried chilling his milk, he doesnt like to drink it either. He's very fussy. I noticed his gums became white on both sides at 3months, and now, on top of the whitish gums, there's a pimple like/whitehead/canker sore looking thing that emerged. He just had his well baby check up and the doctor checked his mouth, did not say anything though. Does anyone of you experiencing this aswell?