I have a different answer.
Pregnancy must be ruled out. You should not go to the ER without this in mind, since you need to avoid any radiation [x ray] until they run a blood test called beta HCG.
You did not say lower abdomen, you said lower stomach with vomtting, typical of pregnancy.
Also typical of ulcer. This would be a serious ulcer of the stomach, or gastritis typically.
gastroenteritis [viral, or bacterial] can cause upper and lower symptoms.
Lower right symptoms with vomitting can indicate appendicitis...a complete emergency.
Also, what has not been mentioned is a reaction to the flu shot, due to the obvious proximity.
If this is the case, it needs to be reported. Most doctors will not tell you this, but up to 15% of those who get this vaccine have vomitting. Here is a complete list of side effects for one of the typical flu vaccines.
Such reactions are vastly under reported....
See a doctor now with these answers in mind.
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