Could Change In Diet/exercise And Stress Alter Menstrual Cycle?

Hi,

A month ago I had sex for the first time with my boyfriend. He wore a condom and he did not ejaculate. It barely happened for five to ten minutes before I asked him to stop. A week or so later, while i was travelling i got my period.

This month I have not gotten my period and I am getting worried. At the same time, however, this entire month I have changed my diet and excercise. I was eating very little and excercising for up to 1 to 2 hours a day which I am not used to. I also travelled this month and have been under a lot of stress.

Please tell me, is it possible that I am pregnant? Or are the the changes in diet and excercise, along with travelling and stress what have caused me to miss my period this month? What should I do?