Should my birthmark be hurting me / have a tingling feeling?

I have had an indented birthmark on my back since I was born. The doctors say it's nothing. It is slightly blue in colour with a line across it that looks like a stretch mark. For a while now I have been feeling a tingling feeling in the birth mark which is extremely annoying and it occasionally hurts me. I went to the doctors about it and she told me it was just because I was growing, but as I am 17 I am passed my growth stage. I am just worried that it is something more than 'growth' related?