Why?

Why do I have such a hard time accepting a compliment? It's so weird....people will say something nice to me and I will say think you, but in the back of my mind I'm thinking that they must be lying or laughing at me for thinking they were being nice. For instance, I just got my hair highlighted with fairly light highlights. I've had probably 10 people tell me how much they love my hair but I can't help but think they must be saying it just to make me feel good. I see this as such a character flaw and I hate being like this. I want to be able to take a compliment and feel good about myself when people are nice to me about something. Why am I like this? I know I don't have the best self esteem but I didn't know I was this bad! I need to get a grip!