It is not uncommon for an occasional cycle disturbance. You seem to be experiencing one of such kind. Yet, you can exclude pregnancy
by getting a home pregnancy test with a fresh sample of early morning urine and if that is not convincing, repeat the test after one week or go for a blood test
and a sonogram. Also, avoid stress-as stress, weight disturbances, changes of life style tend to interfere with menstrual cycles. Maintain a healthy body weight and eat healthy. Good luck.