Loss Of Speach

3 weeks ago I suddenly was unable to speak. I knew what I wanted to say but when i went to speak it felt like my mouth didnt know how to form the words. over the course of a couple weeks my speach came back. It was still dificult but much clearer. yesterday it came back again and I was unable to speak and it is hard forming words. when this first happens I feel hot, a little dizzy and nauseous and my jaw and mouth area feel weird, but then other than the speach problem I feel ok. I had a ct scan to check for a stroke but nothing was found. the doctors dont know what to check for cause I really have no other symptoms. I did have neurological west nile virus 2 years ago which left me weaker on my right side, muscle spams, vertigo and I get exausted very easily.  So unfortunately these symptoms are normal for me. However the speach thing is new and it makes no sense to me why it showed up suddenly and comes and goes?!?!? Any suggestions as to what might be the cause of this?