To simplify things you have 2 choices, Toby:
Make an appointment with the GP and ask for a sigmoidoscopy
Make an appointment with the GP and ask to be referred for psychological therapy taking into account your AS diagnosis.
Make an appointment today for the earliest possible date.
We don't need to know about your bowel movements on here. We would really like to hear that you have made that GP appointment. Don't remain stuck like this because you don't want a lifetime of this literal cr*p when you can at least try to make things better. Get your Mum to support you-she will only want the best for you and that's not endless interaction on here with strangers.