Dificuldade ao falar inglês

I've been studying English for 8 months and sometimes I look for my biggest troubles in English, especially when I speak it.
I write English so much better than I speak. I'm not saying I don't know how to speak, I really do, but slowly and thinking of the correct words, I mean, I try to remember the words to use in a certain moment. The words come out but after some seconds, this is why I know how to write better than speak, because I have time to think of the words that I have to say.

My question is:

Why don't the words come out right away in my mind when I wanna use them?! I mean... When I wanna talk about what I did during the day or some stuff like that... Even though I know the words?!

Eu sei as palavras mas na hora de falar não vem rápido na mente.