I have missed my period twice going on 3. took to pregnancy tests came back negative. also took tests in er negativave as well any ideas?

Abnormal periods: Many things can affect the menstrual cycle, anything from excessive exercise, to obesity, hormonal changes, nutrition, medications, stress, and more. See a gynecologist if you are worried. Consider starting contraception if you are sexually active. This can help regulate your cycles, but first go see a doctor to find out why they are so irregular.