Thank you for your info! I had read something else about vascular problems after I posted this first note. That is a very strong possibility. Yes, I am female, BTW... I will have it checked out. Again, thank you so much.
The problem may not lie with your intestines. I'm no doctor, but it sounds more like a vascular problem. Are you having migraine headaches with auras? Veins are muscular, and for whatever reason, they can clench down and slow the flow of blood enough to cause first the horrible headache and then both vomiting and diarrhea. That would also explain why you get these headaches with sex. Also, when you eat, blood flows to your digestive system, further slowing the flow to the rest of your body - like your brain. If you already have a vascular (vein) issue, it can bring on the whole cycle again.
I had the same symptoms as you at puberty and with perimenopause, and it was all due to hormone fluctuations. I'm guessing you are female? If so, start with your gynecologist and get your hormones checked. If all that checks out, then it's time for a neurologist and maybe even a cardiologist to take a look at you.