I just had SEX for the first time and I'm having the same issues. I have been in my room in bed laying on my side because It hurts so bad. I feel like I'm dying....
I don't think it has to do with the sex. My daughter has that problem often. I took her to the dr. I suggested they'd take xrays because prior to this last visit she had same problem. She wasn't having normal bowel movements which caused her tummy to fill up. She had same pain as you describe when she ate along with a tummy ache. Just figured I'd tell you bout it. Somethiing to keep in mind.
There would be no relationship to having sex yesterday unless you pulled a muscle.