What Causes Weakness In Legs, Diarrhea And Vomiting?

I believe I have had the stomach flu and/or intestinal flu for the last 4 days. I have had a lot of of diarrhea and have vomited 2 times in the last four days. T he vomiting has ceased but not so much the diarrhea but now my legs feel really weak . Those are the only limbs that feel weak. If I am prescribed an antibiotic will that help me or do you have any ideas as to why my legs feel so week.