Whadda eat Friday eve? Curry or something with lots of fat in it?
Could be that..
Stay off the fat intake, make everything lean from now on in, rice and potatoes with mixed salad helps but no chilis or tabasco. Stay off the coffee it'll annoy it. No bread cos' of the wheat either. Ride, you'll be fine but no Gels, steer clear of refined fats, butters just about ok.
Should be fine by Weds.
Then kill it all over again.
Your tum will recover and get used to the effort but be careful of the gripe's down below when hacking, it's a sign.
You will turn into Sean Kelly (noted squits incident in the Tour back in the day where he had to ride flat chat for 50k's in shit covered bibs)
All good sensations, I'm proud of you.