Gabor, this happened to me too! Once, I was actually asked if English was my first language (because it seemed like I was trying to find the right words all the time). Haha. Nevertheless, this happened for about a month or 2 and then I no longer had the problem.
You have heard me speak now, it never seems like I am trying to find the right words, right? As long as you are not stuttering, you are IMPROVING. Have patience, it will not last long!