Hi
There are many reasons for delayed periods the most common of which is pregnancy. As you say the test is negative I would suggest the following.
Next Steps
do a serum
beta hcg test which is the confirmation test for pregnancy.its a blood test.
after that get an ultrasound done of the pelvis.
pls share these reports with me so I can guide further.
Health Tips
stress, weight loss or gain, hormonal imbalance can cause delayed periods. I strongly suggest u do the above after which I can give u medicine to make ur periods come. once they do we can do some blood tests to find out why such delays are happening.