3 mile warm up loop, poop, then do your workout.
You may have a stomach bug that is going around.
I ran a 50k earlier this year and my stomach started going south about 10 miles in. Each gel and sports drink made it worse. I held up pretty good until right after the last aid station at 26 miles. The course was hilly and probably long so I was already running longer than I anticipated. My calves started cramping and finally both just gave up. I could jog the flats and downs but had to walk up the smallest hill. At 28 miles I couldn't contain my bowels and had to jump off the trail. Unbelievable how hard it is to dig a small hole and lean back against a tree with your calves going so hard into spasms you might not be able to get up after you were done. I was imagining the rescue crew having to pull me up out of my pile of poo and crawling the last 3 miles to the finish. I somehow found a couple non-poisonous leaves, put out the steam and pulled myself to my feet. The last 3 miles wasn't pretty, but I was able to avoid any crawling. After numerous trips to a proper porta potty, I finally felt good enough to eat something about 5 hours after the race.