My English writing skills are very good, yet I can't speak fluently, what can I do to fix that?

Find people to practice with even if they're not fluent. Even if they can't speak English well, it will give you the opportunity to practice speaking to someone. 

If you don't want to do that, maybe just record yourself on your computer making up 'conversations' as if you're talking to someone, and then go back and listen to your recording. Speaking out loud should be your first priority.

If possible, watch English language tv shows or movies and try to imagine yourself being in the conversations and speak out loud how you would respond if you were talking to the other person.  

The trick is to get the 'language' part of your brain to be able to think in the target language rather than in your native language and then translate it to English. 

Practice as much as you can, choice favorite subjects to talk about, expand your vocabulary and use phrases not words.

you need to achieve your social goals using evidence-based exercises, techniques and training methods.

speak clearly-develop flow-choose your mastery topics-practice daily-practice at events

To become fluent, you need to be able to speak without pausing to think of the correct words and sentence construction and

try to read more and more

To be able to speak English fluently, i advise you to read English books as much as possible, and focus on writting, listening and speaking, eather to others or just with your self. as well as, focusing on english pronuctiation courses which can help you to investigate or to know how words are proununces in english, i'm sure that if you follow all  these steps and if you keep doing it  and becoming accustamed of that every day,  you will be a native speaker in english.

First,you have to know something which is NO thing is difficult at all.It's really good you are skillful in writing.For listening you have to listen more and more in order to speak well. Believe it  or not, Practice Makes Perfect, listen more you speak more .

try to talk even to yourself ,be crazy ,at the end, you will notice what i have said .

The thing is you have low self stem and low self confidence. You are skilled already in writing and it is easy for you to speak fluently yet you are not isn't it? Develop your confidence and convince your self that you can take out from your shell  without anybody's help. To make it , is a constant practice through your peer or make as your medium language to your daily conversation. You can also select an interesting topic with you and develop it on the spot in front of the mirror then deliver it as far as you can. Always try to speak it , for in this  way you will develop confidence and trust to yourself. Later you will discover that you did it perfectly. Thanks

I advice you to start to listening to an English song find the lyrics and sing with the song many times during that it's good to understand the meaning of it .  repeat this with other songs.

you can start with easy songs then fast songs for this purpose.