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After going through your history, you have missed your period it could be related to your weight loss
, exercise and stress. You have taken urine pregnancy
test and it is negative.In such condition hormonal imbalance can cause delay in period.
Your chances of pregnancy depends on if you had unprotected sex or not if there is any chance then you can go for blood test
of Beta HCG which will confirm that there is no pregnancy.
You can consult a Gynecologist to examine you and rule out pregnancy than your amenorrhea
may be treated accordingly.
You should also get urine analysis done with bacterial culture and take treatment of Urinary tract Infection
Hope this helps.
Dr.Akhilesh Dubey M.D.