bitcoin slowly went down this year, from almost 20k USD last December and went down at a significant price
what might be the reason why bitcoin's price is going down?
what are the major things that can greatly influence bitcoin?
answers would be fully appreciated

Bitcoin's astronomical rise in 2017 paved way for a lot of new stuffs in cryptocurrency world, such things as Bitcoin Futures -which inadvertently has contributed immensely to the below-9k price of BTC this year and even more recently, the whole FUD and heightened expectations from G20 meeting scheduled in July would be a huge milestone.
We are still waiting for the right time when Bitcoin finds positive sentiment. Various news that exist today does not show that Bitcoin will get good news. But we must still believe that the future bitcoin will get various support, as long as we continue to use bticoin then it is expected Bitcoin will continue to increase. So do not ever be pessimistic because it will make things worse. Bitcoin prices can get recover when we are getting routine use it.