Weird Changes ; Pregnant ? Answer ?

so i had sex june 21st & it just happened to be the first day of my period and then a day or two later it stopped. then a day after that i had pink/brown spotting for one day then nothing at all its just back to its normal cleansing discharge . i talked to my boyfriend and he said that he didn't c.u.m but there was p.r.e.c.u.m ; perhaps he came without him knowing since i was on my period? anyways my question is could i be pregnant ? i'm having pregnancy like symptoms ; headaches , peeing alot , dizzy, can't stay standing up , feeling sick all day (nausea) , and ALWAYS sleepy. i know there's not way to find out for sure without taking a test but i need some answers to reassure myself before i actually go and buy one for no reason , answer please? thanks .