Still jealous after 6 years being together...

I've been with my wife for 6 years. We have 3 kids (2, 3, and 5), and we're in our mid twenties. Our marriage is AWESOME. 100% trust on both sides. We're affectionate toward each other and are very happy. No issues...except, I still can't get over her past. She's had about 13 different partners before me. I had 1 before her. Whenever she mentions someone she knew from high school for some reason (saw them on FB, someone getting married, etc), I can't help but to ask if they had any kind of history, and it burns me up. This isn't her problem, it's mine. She hasn't done anything wrong, and as much as I honestly don't show her that it upsets me, inside it does. I'm not controlling or anything like that, I encourage her to have a social life and go out and make friends. She just started working after a few years (she has been a stay at home mother), and I am so happy for her to get out of the house and meet people and have a life...but I'm insanely jealous! There are no troubles between us, no trust issues, we've never cheated on each other...I'm just a really insecure person. Up until this point I've just ignored and buried my jealousy and insecurity, but I think after 6 years there must be something that I'm doing wrong. Something wrong with me. It can't be normal to be jealous after so long. Thoughts? Should I talk to a professional counselor or something?