What Causes Delayed Period And Vomiting While Having Implant Inserted?

My daughter is sixteen and had the implant for birth control for two months, she has not had her period and is experiencing nausea and vomiting. She just informed me she had protected sex two weeks after the implant was inserted. She was already on birth control pills before the implant. I am almost positive she cant be pregnant. Please tell me I have nothing to worry about her being pregnant.