Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Missed period is commonly believed to happen in those who are pregnant. It is a cause if you are sexually active. As you have done the pregnancy test 3 times and at laboratory also and resulted negative. So it’s least likely. But can be confirmed by doing a USG abdomen and pelvis. Also, it is a concern that you have developed pregnancy symptoms, but test resulted negative. Meet a gynecologist in clinic as soon as possible. Many other causes are there for the missed period except pregnancy. Those are: 1. Excessive sudden weight gain or weight loss may lead to missed period. 2. If you are under any birth control measures, then sometimes it’s likely that you may face irregular or a few times missed period. 3. Any pelvic organ diseases like polycystic ovarian disease can lead to missed period. 4. Hormonal imbalance in your body. The functioning of menstrual cycle is predominately affected by the change of hormonal environment and hormone-related diseases like thyroid disorders. So, you should not delay more to consult a doctor and get these evaluated. You need to do few tests and those are CBC, serum TSH, T3, T4, USG abdomen and pelvis. Visit a gynecologist in a nearby clinic and get evaluated to start your medications. I have answered your query. Let me know if I can assist you further. Regards, Dr. Anuradha Das