Hello Mamta.
      As u told u r having 
pregnancy of 6 months and as per the scan report the placenta is 5.6 cms away from os.
     Firts I tell u that remove the fear from your mind that it is abnormal. As per the obstetric experts the low lying placenta is of 2 - 3 cms away distance from os.
       5 cms are normal site for placenta, and as pregnancy proceeds the placenta migrates upwards normally.
      And about exercise.... Please take adequate 
bed rest with regular house work. No extra exercise recommended to you because exercise worsens the condition. Avoid weight lifting and frequent intercourse.
      Normally there is little pain abdomen continuing throughout the pregnancy till after delivery.. No extra medicines needed. You may take T Paracetomol (500mg)as per need not to exceed three tablets daily.
      You may get the blackish striae on abdomen, 
acne on face as normal consequences of pregnancy, so dont fear.
     Take high protein low fat diet. U take 
carbohydrate drinks, fruit juices etc as routine
     Have a usg scan at 7 month and at 8 1/2 month