You are young and your pain is in the middle of your back. This is not the usual site of pain for the young people but the mode of onset of symptoms can be explained by your pulling down a heavy luggage. I hope you have no other symptoms like fever, weight loss or joint pain. Such pain could also be brought on by long bumpy ride in a vehicle. Usually there is some muscle or ligamentous has strained that causes pain. In the back this may take about six weeks to heal. So, don’t worry it will settle in due course of time. Medicines are not important but you must avoid carrying heavy luggage. If this is the cause of pain it should settle in due course if this is not the cause it will not settle. Then you will need investigations. Keep medicines only on as-and-when required basis. Safest would be Paracetamol 500 mg two or three times a day. In case you have persistent pain you will need x-rays of the back.