The main factor is the demand and interest of the people on Bitcoin. Once the demand and interest of the people are high then the value is going up and same goes when the demand and interest of the people is low, then the value is going down. That is why FUDs and false news are affecting it because it those things can affect the interest of the people on Bitcoin, that is why it is not really advisable to take actions based on emotions because you may create more damage than a solution, example panic selling.
behind rise and down demand interest there is important news.if it's news good for bitcoin , demand interest will increase in market.but if fud's coming , it can make selling interest increasing.and make price goes down.