You have to go back to the hospital and ensure the stitches are done properly. You can use a sitz bath with epsom salt + warm water. Seat for 2 times a day, 15-30 mins. This is to subside the pain and slowly the stitching thread will dry and fall by itself. However, within 2-3 weeks not recover from the period you give birth, then ensure that you have it thoroughly check and proper medicine/spray to heal the tearing.