Oddly late period

Morgan

I haven’t had a period since December 13th.. I had a pregnancy test done at the doctor and it came back negative. I’m no more stressed than usual, only 22 so not menopausal. I have started eating better and losing weight, but nothing rapidly or extreme. I have an OB appointment on February 14th, but the wait is killing me. I’ve never been more than a few days late. What are some things that could be causing this? Google is no help