There are two types of surgery which result in a Colostomy:
APER (Abdomino Perineal Excision of Rectum) - involves the removal of the rectum and anus
Hartmann's resection - the rectum is left in place
If the rectum is still in place the pain can be due to a build up of mucus. The pain can be a low back ache, a sensation of pressure in the rectum, sharp shooting pains or feeling the need to go to the toilet. It may be possible to evacuate this mucus by sitting on the toilet and gently bearing down. Alternatively your stoma care nurse or GP may suggest a suppository. It is a normal function of the body to produce mucus.
If you have had an APER and your rectum and anus have been removed you may still have the feeling you need to open your bowels or experience pain where your rectum used to be. This is known as 'phantom rectum syndrome'. The exact cause of the pain is unknown, but it is quite possible that the nerves around the rectum may have been damaged during surgery. Some people will find that paracetamol will eliminate the pain. If it is more extreme, then it is worth discussing with your GP the possibility of a referral to a chronic pain team.
Any new pain should always be reported to a GP, surgeon or specialist nurse so that rare, more acute causes of pain eg an abscess or hernia can be ruled out.