Nine month old baby girl having black spot on her lower lips

Hi

My nine month old daughter have a black spot on her lower lip for the past one week. it slowly growing by size. yesterday we went to a pediatrician and consulted the same. He asked few questions

1) Was the spot reddish in the beginning
2) Does she have itching
3) Does she rub the lips
4) Does she show any irritations

Answer to all these questions are NO. Pediatrician had a look at it and told may be its an insect bite. Today another black spot is shown on her lower lip, i am worried about this.

Is this common in infants or we have to consult to a skin doctor

Kind regards
Saji