*me mysteriously appears in a puff of smoke*
I jogged for 3.5km.... then suddenly, I got sharp pains in my
tummy.
They wouldn't go away.... apparently, my dinner was still
undigested in my stomach even though I ran two hours after eating.

I had to walk the 3.5km home - with a stomach all tied up in
knots. 
Might be "air" in your stomach....
I kena before.