is this implantation bleeding? spotting?

i did have sex on oct 5 & 7. it was unprotected and he did pull out. i am on the arm implant birth control. saturday night i went to use the bathroom and noticed that there was some dark brown discharge (kindve heavy), and i woke up sunday morning and there was only 2 little spots. there was none this morning. is this implantation bleeding? my period according to eve comes in 2 days... i took a pregnancy test today and it came out negative. please help!!! i'm very scared