Hello, I can understand your concern for your symptoms. 1) Your symptoms are not typically identical with flu symptoms as you have not developed any episode of fever, general body ache. 2) Back sore might be due to retching for forceful vomiting or also may be due to vomiting induced weakness. 3) For you, frequency of vomiting in such short interval is concern and mostly it might be due to irritation from particular, partially cooked or raw food ingested day before. This can cause severe inflammation (redness + oedema) to inner wall of stomach which sometimes extend to start part of small intestine. This condition is known as gastroenteritis. 4) This is not serious problem unless you have profuse vomiting which leads to dehydration. In such scenario, you must get hospitalized to start IV fluids and injectable therapy. 5) Medication for acidity, medication to prevent vomiting, antispasmodic medications, light diet with adequate amount of liquids is the treatment of mild gastroenteritis. Hope I answered your query. If you have any further doubts, I would be happy to help you. Have a nice day!