iv suffered with horrific IBS over the years. i have some truley disgusting stories i could share, but il stick to the usual - it hurts and its hard to control. unfortunatly i never found my food trigger. it comes and goes from time to time. my dad also suffers with it. could be a stress thing but it doesnt really tally with me what mood im in.
it COULD be an intollerance, but it could also just be a bit of a shock to the system. if uv been eating mostly red days, which is alot like the atkins diet, the only carbs and fibre ur getting is from what ever veg. i would suggest introducing pasta etc into ur diet slowly, bulking it out with more veg. i personaly think cutting it out all together will inevitably leave you constipated if bulk of every meal is meat.
tyr experimenting urself with trigger foods, and if u have no joy, you can always pop to the GP, who may prescribe soemthing like, or similar to a drug called colofac, which is for IBS. plus, if youv already spent time experimenting with different foods, then this will give you more to go on with the gp. iv known so many people (including msyelf) who went , and the first thing they say is "go away and try a wheat free diet" etc.
i wish u all the best, as i know what a pain IBS can be. i hope you do find a trigger so al u have to do is cut out that food.