Missed 2 periods but tests are negative

So I've been logging and realized I was a few days late. I started taking tests once a week just for peace of mind. Well, they're all negative everytime but I never got my period. Now I've seen that I've missed a second period. I am still taking tests and they are all still showing negative. I have been pretty stressed lately. I've heard that can affect your cyle, but 2 missed periods seems crazy. Also missing them isnt helping with the stress levels at all. Any idea or similar occurrence for anyone?