Don't worry, wait for another 5 days and repeat urine Pregnancy test. Or if you r more concern do sr beta Hcg. If negative then meet gynaecologist. Sometimes it happens due to stress, anovulatory cycle, lil hormone changes also.
Your menstrual cycle is under hormonal control. The ovary usually releases one egg (ovulation) each month, and about two weeks after, the uterine lining sheds, resulting in menstruation. If the egg is fertilized, it is implanted into the uterus and menstruation does not occur. However, if ovulation does not occur regularly, the body does not send signals to the uterus to regulate menstruation. Stress, jet lag, lack of sleep and too much exercise can disrupt your hormonal balance and cause a change in your usual menstrual cycle...Consult gynecologists they will do the needful.
Wait for 4-5 days and repeat a urine test.If its still negative, consult a gynecologist for the needful.
You can also visit my clinic International Fertility Centre, that offers best gynecology services and ensures you a successful treatment.