Hey doctor My girlfriend and I had sex about two

Patient: Hey doctor. My girlfriend and I had sex about two months ago. She took Plan B the next day. About two weeks later she had her period on schedule but it was very light, about two days. She was supposed to have her next period around this time but has not. She has been under a lot of stress lately with a lot going on in her life. She took a pregnancy test and it came back negative. Is there anything we should be worrying about, because having a baby right now is not exactly ideal.

Symptoms: Stress, Late period

Doctor: