The symptoms you describe are somewhat vague and
may or may not be caused by the prednisone
. You have had a relatively short course of treatment, so it is unlikely that there are permanent effects.
Nausea can be caused by various diseases of the upper GI tract - such as GERD, inflammation, an ulcer, as well as liver and gallbladder disease.
Fatigue can be caused by a myriad of diseases - including anemia, kidney disease, dehydration, thyroid disease, as well as electrolyte abnormalities.