Hello,
If the blood tests have come up negative chances of pregnancy are less. These symptoms of missed periods can be due to secondary amenorrhea. Causes of secondary amenorrhea include stress and anxiety, malnutrition, depression, overexercising, sudden weight loss or gain (obesity), thyroid disorders and hormonal imbalance due to polycystic ovarian syndrome(PCOS).
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
you best bet is to look up pregnancy blood test in your area if you want to be sure.