Welcome to HealthcareMagic. First of all i would advice you to hold whatever physical activities you were onto untill fully diagnosed.The problem of shaky legs or weak legs, are they very recent. Do you consider it as weakness or trembling? Is it more proximal ie..more towards the hip or something restricted to below the knee? See it could be something of muscular/neurological origin. Get initially your salt/ electrolyte-sodium/pottasium/calcium etc levels checked, as these are very common cause of this kind of problems.If you find them normal and your problem keeps bothering you more, then further your queries to neurologist
.Get well soon.