Mt gox news and sec news have the most effect on bitcoin for me, a lot of weak hands and also fud make it worse. It can really decrease to $3000 with panicking people.

I think Mt. Gox has the biggest effect on the market price right now. Followed by different FUD about bitcoin and panic selling also contributed on the current market situation. More and more people are dumping because of the news. So, I guess it will take some time before the bull market starts again.

In 2017 there was a panic selling since many have joined btc in hope and with a dream of getting a profit. Thus due to that high demand bitcoin went up to 20k$ but the correction started and the value fell down. After the correction you can blame it to facebook, google and twitter since after their announcement bitcoin had suffered another red market.

False FUD created by regulation issues do the most of it (very unjustifiedly) + some other things like problems with exchanges, however, the move was actually pushed by as a normal yearly movement - after a lot of "end of year" investments there comes a phase of consolidation after the New Year. However, since with Bitcoin everything is so dramatic, the rises and consolidations look more like overhype (which they actually are) and total breakages.

Also, there were no substantial real developments over last few months so there was nothing "tactile" to sustain the opposite movement.

I also suspect that the centralization is doing its part.Big investors and whales are actually driving the price up or down to get richer (they can do that with big buys and big sell-offs -they push the price up or down and also create panic euphoria since their moves are constantly being monitored by the society).

It was the decision of the big whales that created a panic selling wave in the market and since we don't have that level of experience and maturity which is required to sustain in such situation, it creates more anarchy in the market is something is happening on higher level so I do see this main reason behind the current market situation.

The sold bitcoins of Mt Gix really affected the bitcoin's price, as I've saw it in an article. Now, I understand that bitcoin can manipulate ny whales easily. There are some factors influence the price of bitcoin and one of it is called as cartel. But right now, we can't say it is kind of cartel because only one person control the price indirectly.

Not everything can keep up the market up all the time.
There always comes the time when high peak has to go down for better start up and new finish line. Bitcoin is already gotten strangled with storms of bans, illegal tender and summit meeting agree/disagree kind of stuff and much more.
Whales dumping the bitcoin whenever they want because of no control over how much and when you can do that!
Off course the net effect would be crushing of the market.

bad news, bitcoin theft and a country policy ban

It is usual that this is what affects the price of Bitcoin specifically. Bitcoin prices will always change at any time and no one will be able to know the price movement of Bitcoin. The demand and supply factors are the major factors that will affect the global Bitcoin price. So for anyone who wants to participate in the development of Bitcoin, it is necessary to transact more often with Bitcoin, it will increase popularity and Bitcoin price will increase slowly.