I would avoid lifting anything heavy and apply ice for the swelling. I see no reason why you should not have sex as long as you take it easy.

thanks for answering my question

Sudden episode of back pain is commonly a result of weak core muscles and improvement-needed posture. In general, the recommended current treatment practice is rapid return to normal activities (despite the pain). Bed rest and other previously used practices has not shown any advantage. However, it is highly recommended that you see a physician to make sure there is no additional underlying reason for the pain. Please note that if you are interested in preventing future recurrence, strengthening core muscles (deep muscles in the abdominal area) is the most effective mid and long term approach (i.e. it will not help you with the current acute pain - but sticking to an exercise routine should reduce pain recurrence and allow faster return to normal activity). Taken that you do see a physician, you might want to strengthen your core muscles following Pilates or Pilates-like exercises or similar exercises subscribed by a PT. These exercises are shown to be effective in fixing bad posture and therefore preventing posture-related pains. We have a lot of positive experience in treating patients using these methods. The important thing is in correct execution mainly in terms of "keeping" the abdominal tight ("naval to spine") - you can see a demonstration by searching Pilates sites or on YouTube.