It was so low last week and people started to buy it because of potential rising. We say it market cycle and market psychology. And it works everytime.
Supply and demand I am sure, this is the case that is only responsible for the price being jumped so high and then going down every other week. In international market, there is a fix supply of bitcoins that is have been spread over the world. But yes, demand is increasing day by day. So when there is shortage of coins, or people when bought much, market demand increases, and hence prices get higher.