Lack Of Creativity

Lately when I have been in art class, I cannot think of anything to draw or paint. I was looking for some inspiration around my room and I came across my grade 9 sketch book. I looked through each and every page and I wasn't very impressed with my artistic ability but I was suprised at how creative I was. Every single page had something on it and there was lots of colour and designs and the sketch book itself was superrrr heavy. I don't know why I have had such a lack of creativity. It almost makes me angry. I think my problem is that I want everything in my sketch book to look good but if I don't think I can make my "vision" a reality, it isn't even worth trying. Which probably isn't the greatest attitude to have as art isn't about everything being a "masterpiece" it is about improvements.