These include stomach disorders such as
gastroenteritis, liver/gall bladder disease, cancer, medications,inner ear diseases like labrynthitis,
ulcers/gastritis, metabolic like diabetes,hypothyroidism and adrenal diseases or neurological causes.Cyclic vomiting syndrome is also stated to cause constant nausea.
I will sincerely advise you to consult a physician and get these possibilities ruled out one by one.