Sorry I have been awol - busy with work and home and general life 
Roastie I saw an article in the DM (sorry!) yesterday about stitch and why it happens and what you can do to prevent it - didn't read it properly but thought you might want to google it and see if it is any help to you?
I have always suffered from stitch when running (gave me a hate-relationship with running for about 30 years!) - when I started going to a running group 3 years ago to combat my running issues, I still suffered. However, it gradually stopped - no big 'aha' moment, it just gradually stopped happening and I am not sure if this was just because my body was getting used to running as an exercise, I was getting fitter - no idea. Was able to run 6-10 miles without getting a stitch.l However, I stopped running and, as I said, went for a run for the first time in months last week and lo and behold, I got stitch
No idea what I am trying to say but just thought I would share 
roastie sorry the wheels of the NHS are turning slowly for you, it is so frustrating isn't it? But, on the positive side, just think of all the other forms of exercise you have tried that you probably wouldn't have done otherwise.
Still going with my 21df/21dfx schedule. Can't decide which is the worst workout - Dirty 30 extreme, cardio fix extreme or total body cardio. Hate them all in equal measures I think
However, I am able to hold plank for longer, managed 10 full push-ups this morning, am using slightly heavier weights on upper fix so small improvements are happening.