Spotting or implantation

Claudio
My gf recently started take birth control for the first time a month ago and the doctor told her spotting would be normal. We had unprotected sex a few times in the last month and lately the past 4 days she's been spotting looking like reddish brownish. We took a test two days ago and it was negative, are these just spotting from the birth control or implantation bleeding?