welcome to justanswer and thanks for your question,
whats your age?
any past history of gastrointestinal diseases?
taking any iron suppliments?
Nausea with pain in the stomatch area may indicate GI tract inflamation ,however black stools may indicate bleeding from gastrointestinal tract (may be due to ulcers), feeling of ice going through veins may be due to constriction of skin's small blood vessels (occurs in case of anxiety "or" a defensive mechanism of the body to prevent heat loss, however in case of GI bleeding ,perepheral constriction is also seen,so as to mainatin the total volume of blood in the body),therefore i suggest you to visit your doctor to have some diagnostic tests done.
meanwhile i suggest you to avoid any hard foods, BRAT diet ie banana,rice,applesauce and toast will help ,you can also take supplements such as psyllium (Metamucil) or methylcellulose (Citrucel) with fluids ,they increase the bulk of stool, BUT as i said visit your doc for diagnostic tests.
yes, its possible that in contrast CT scan some ulcers may not be visible, in this case the preferred methods is Endoscopic examination (in this method doctor can directly see the surface of gastric mucosal layer and detect any scars /ulcers)
also there are some other tests like stool antigen test, breath test etc.
Symptom of black stool + abdominal pain may indicate GI bleeding, a consultation with a specialist is must in your case.
i hope this information is useful,