A lot of things affect whether your period may be delayed, diet can be one, sometime for months. You can read this article written by Merely Me, the community leader here, about that.

If you took Plan B the next morning, you probably aren't pregnant. The thing with morning after pills, the closer you take them to having had intercourse, the more effective they are. They are not 100% effective, no artificial birth control method is, and their effectiveness declines with time.

If you followed the instructions for the hpt's and waited to take them not sooner than a week after your next, normal period was missed, then they should be good. Sometimes, an hpt will not pick up an ectopic pregnancy, where the egg embeds itself somewhere other than the uterine wall. So if you have pain and other symptoms you must see a doctor.