What Causes Abdomen Cramps With Brown Spotting?

i am 23 i have just had a very light period which started with brown spotting and had unprotected sex on saturday i now feel sick etc and had some cramping, but i also feel pain in ovaries. Not sure if it wasnt my period but spotting before but it lasted 6 days like a period and if the pain im experiencing now is due to pregnancy implantation or my actual period about to start?