Taken Plan B, Suggested Birth Control Intake, Bleeding Lightly, Headache, Back Pain, Dizziness. What Is Wrong?

Hi, I took a Plan B pill and my doctor said to start my birth control on Sunday. I woke up late so I figured I ll just start it the next day because she suggested taking it in the morning rather than at night. But that night I started bleeding lightly, so I didn t start the pill the next day. I normally get dysmenorrhea for the first to second day of my period so I didn t think anything was wrong, just that it was really bad yesterday. I had a headache. I was dizzy, had lower back pain and thought I was hungry because of abdominal pain . I was also sweating even though I felt it was cold. After eating I threw up and I just thought it was the dysmenorrhea. But I feel the same way today, except I haven t actually thrown up. And it s weird because I m on my third day. I should be fine already, but I m not. I m not sure what s wrong. I really want to get better. I had to leave work early yesterday and I have to go in tomorrow.