Public Display of Affection...?

So i've been married for over 3 years, and we never had a problem with PDA. But apparently my wife doesnt like to kiss in public..Now I'm not talking about pionate kisses...just a regular kiss. Whats going on? I see regular couples kiss all the time..I mean, are we going back to the old high school days where we're not allowed to kiss each other in public. Shouldnt couples, especially married ones, be able to kiss in front of people without being ashamed...i dont know if shes embarred by me or what...