That doesn't sound normal. Get in touch with your stoma nurse or your surgeon and tell them what's happening. I had an ileostomy for two years; it would occasionally get backed up and then clear itself after a few minutes/hours. It's normal to occasionally get backed up with an ileostomy, but not all the time - you need tests to find out what's causing it.
Also pay a visit to the Ostomies board. On page 2 there is a topic by SolomonSeal - he had similar problems to you and it turned out to be a mechanical issue. He got relief through a surgical revision to the stoma.
Dx Crohn's in June 2000. (Yay )
Tried: 5-ASAs, azathioprine, 6MP, Remicade, methotrexate, Humira, diets.
1st surgery 20/2/13 - subtotal colectomy with end ileostomy.
2nd surgery 10/7/15 - ileorectal anastomosis. Stoma reversed and ileum connected to the rectum.
Current status: Chronic flare. Do I have any other kind?
Current meds: 50mg 6MP; Entyvio (started 3/11/16)