for the last 2 years or so my arms and legs have felt really weak, i also feel asthough im loosing weight eventhough i eat a balanced diet and eat correctly, i feel dizzy some of the time, and i find it really hard to concerntrate, iv been to my gp but they all say im depressed or its in my head and personly i know something is wrong i just cant find out what, iv had blood tests and everything is fine, please help.