[Coffee.]

Everything Always* said is correct. I'd add if you're American, your insurance should cover birth control costs, and there are clinics that can help you find birth control options for you as well. While pregnancy is possible, if you used a condom without issue, I would try not to worry so much as worrying about potential pregnancy may be throwing off your period (causing you to worry more...it's a bad cycle). That major stressor may be influencing it as well. As Always* said, take a pregnancy test two weeks after your last sex act. If it's negative, I think it must be stress, and I'd consider seeking counseling or anything to help you through that. Good luck!