What Causes Dizziness And Vomiting While HPT Is Negative?

Hello i am a 32 year old female and right now i am having lots of dizziness and headaches and throwing up for the past 4 days i don t know why... the situation is that i took a Plan B pill on the 22 of December and on the 31 i saw my menstrual i finished on the 5 of January after that i was sexually active with out protection and today January 24 i saw my menstrual again can you please help and tell me what is going on i took a pregnancy test and it came out negative. i hope you can help me