Bitcoins value is derived from the market forces driven mostly by its adoption rate. As more people get into Bitcoins and seek to buy them, because its supply is at a constant rate, that adoption rate applies upward pressure on its value. There might be fluctuations from events, news, and more temporal factors but that appears to be the long term factor when the more noisy factors are filtered out as shown in a paper I referenced in a post linked below.

However, Bitcoin's adoption rate has been dropping since late December 2017. If that does not recover there is almost no way the recovery can be sustained. I described in detail where things are based on the fundamentals here and would appreciate your thoughts as well.
https://steemit.com/bitcoin/@kenraphael/bitcoins-have-not-yet-fundamentally-recovered-at-this-time-a-mathematical-case