Hi lilymaud
A pic would be easier to see what you're describing, but it does sound to me like perhaps it should get checked out. You could even just take Olivia to a GP or even just a clinic sister for an initial consultation. They should be able to say whether or not a paediatrician needs to look more closely.
My baby's got a pea-sized one...it's maybe an inch behind his ear, lower head, right side... It doesn'tbother her but I'm wondering.. just discovered it last Saturday.