Good job on taking plan b!
I guess I'm not sure what you mean by not feeling yourself.. Are you sick, stressed, tired, cranky?
Plan b has some weird side effects like nausea, stomach pains, fatigue, headaches, dizziness, sore breast, vomiting, and diarrhea, so if you're feeling a little out of it physically-- then I'd say it's normal. You may also be a little moody (Plus stress of pregnancy or whatever else = really moody)
If you miss your period, then test. But don't panic too much because Plan B has a tendency to mess with your cycle, so it can come really early or late, heavy or light, and still be completely normal. Spotting is also a possibility, but these effects should go away within 3 months.
For the future, you may want to look into another form of birthcontrol. It helps take the am-I-pregnant-stress that typically follows sex out of the equation.
Good luck