Hey I Had Sex 4 Days Before My Period. My

Hey i had sex 4 days before my period. my period was 2 days late then had light to medium period (with is not normal usely it is heavy) for 3 days and 1 day nothing en thrn started again today. i have nausea dizziness tierd all day of and on headache and frequently used the toilet. i tested tested today but not pregnant and slight swelling down there. wat can be the problem