Is it normal that i love doing this?

One day i was home alone and very horny but the internet was off. The day before i had seen my mum naked and she was really hot. I decided to run upstairs and just check out her knickers. I pulled some out of the wash bag and smelled them, before i knew it i was licking her wet knickers and wanking. Afterwards i felt so ashamed of what i did but whenever i get horny again i go and find another pair, Is this normal in any way?