showing signs of pregnancy but I already had my period, though it was shorter than usual

I have been nauseous, violently dizzy, have had a head ache and yesterday I started spotting when I'm not due for another three weeks, I am PETRIFIED that I could be pregnant, as my ex and I arent really on speaking terms. I keep trying to go over in my head all other possibilities for all of these symptoms. I am freaking out. someone please give me some advice, or suggestions. anything is going to be helpful! thanks!