Sometimes 2 days is just not long enough to get better and strong. You need another days rest to recuperate.
You feel light headed because you are probable dehydrated. Best thing to do is to drink plenty of gatorade.
It sounds like to me you may be slightly to moderately dehydrated. When you had the diarrhea and vomiting for 2 days, your body lost a lot of water and fluids it needs to maintain a normal blood pressure. When you get dehydrated to the point you are dizzy, I would recommend getting it checked, because you could get to the point of passing out and such. But, your symptoms indicate moderate dehydration which can cause low blood pressure. I would call my doctor and tell him you may be dehydrated because of the dizziness and low blood pressure and have him re-check you. You may need some iv fluids to get you back on track and some rest, too. Take care and good luck. Hope this helped.