Took plan b a month ago,taking my birth control pill,period came on time, pain under right side of rib.vomiting,nausea. could i be pregnant?

Probably not, but...: If worried, can test. A urine pregnancy test done correctly gives a reliable result 3 weeks after sex (3 weeks after when conception might have happened). If done sooner, a positive result is likely real, but a negative result may be due to testing too soon, and therefore lead to a repeat test. If a woman has her normal regular period, then she is usually presumed not pregnant.