Hi, According to your description the possibility of pregnancy is less as all your pregnancy test kits gave negative results and also you got one menstrual period. Nausea and fatigue can be seen in different conditions like pelvic infections, premenstrual period, etc. As you mentioned stress also can lead to this type of symptoms. If you want to be sure, please go for a blood test for pregnancy. If serum beta HCG levels in the blood test at less than 5 mIU/mL that rules out the possibility of pregnancy. If symptoms persist even after the test, better to get evaluated. By clinical examination and investigations like complete blood picture, thyroid profile, serum electrolytes and ultrasound, the possible cause of your problem can be identified and treatment can be taken accordingly. Meanwhile you can go for symptomatic treatment with antacids and anti-emetics. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Sree Gouri S. R., OBGYN