Is it normal to feel ashamed of my teenage years?

I feel so ashamed of my teenage years. I'm currently 21 and far more improved than I was 3 years ago. Around the time I got my first girlfriend (I was about 16) I had very bad skin (spots and a greyish unhealthy look), I was scrawny, I smelt horrible despite being of average hygiene (a few bad habits kept the smell around but I washed often), I was far less attractive, I was impressionable and I was very insecure.
Now I've got far better skin, I look healthy, I'm still very thin but I've put on small amounts of weight and muscle in the right areas, I'm very hygienic and I smell quite normal now (my only worries are when I sweat after a long walk now!), I'm more attractive, more confident (but still very shy) and far less impressionable.
I feel like a massive improvement and thinking back I feel ashamed of myself in the past. Despite never having done any drugs or done anything violent and being a generally kind but nerdy teenager, is it normal that I feel so ashamed of my past?

Note: I have a theory that my first girlfriend (who I dated for over 2 years) may be the source of this shame. We had a great relationship but she had no problems telling me what my issues were and some of them did strike me deep in the long run. She mocked me for my appearance alot and told me that people had been commenting on my smell (though she did say I smelt fine to her). I greatly appreciate her honesty but I think it may have left me with some lingering shame. Wish she could see how far I've come now. She'd be envious as hell hopefully! :]