What Causes Delay In Periods?

I m 20 years old and I m a virgin, and on no forms of birth control or medication. My last period was on January 12th, and I ve missed a cycle in February, with no signs of it coming this month in March. During the time I was supposed to ovulate in February, I changed my sleep cycle, eating habits, was quite stressed from uni, and was sick with a cold. Since then, I ve been pretty normal and healthy, maybe sleeping a little later than usual, but no more stressed than I am usually. Is there something wrong with me? I have no signs of infection, but I for the last two weeks I ve had my usual PMS symptoms of bloating. Is this normal to skip a period or two? I m frankly quite scared at this point.