Hi Becky!
The advice given to you by the others is excellent.
Do you regularly consult with an Endocrinologist and have regular blood tests done? Is this Endocrinologist very knowledgeable or a specialist in CAH? You need to have a good evaluation as it sounds like your treatment has gotten out of hand!
As the others have said you may need a longer acting steroid like Prednisolone or Dexamethasone.
Also as Kathy mentioned, have you had a GI (gastrointestinal) specialist to evaluate your GI problems? They need to look for Crohns, Coeliac (blood tests and biopsy during colonoscopy) and other disorders like Ulcerative Colitis etc.
I don't think I have come across 24/7 diarrhoea in high dose steroids - it could well be another disorder altogether causing this....but you need to get your CAH back on track....of course 24/7 diarrhoea will not help the steroid absorption either. Will only worsen the problem.
Keep us informed!