Why Am I Having Cramping Pains With Vomiting?

I am having mild-severe cramping pains. My period was 8 days ago and it only lasted for one day. I have also been throwing up on and off for the past week. I do participate in unprotected sex and I have several times in March. I just took a pregnancy test this morning and it came back negative. I am not sure if I should go to the doctor to get one or if something else is wrong with me.