Skip a period?

Emily
Has anyone skipped a period? I have once before and was told it's because I was too stressed. I think I may have again but I don't feel stressed. I have taken two tests a week apart and both have come back negative. Am I not waiting long enough to take the tests? Today I am 15 days late. Trying for our first and I am tired of getting my hopes up. Should I see a doctor? I guess I just don't know how this whole thing works. Any help or encouraging words would be greatly appreciated.