Need advice

Unsure what group to post this in. I'm day 32 (1 days late) for the last 4 days I've had really light brown spotting which I never get! It stop yesterday afternoon so more 3 and a half days... I'm 12 weeks pp (already had my first period) me and my partner use condoms but before we actually have sex we mess about and pull out before he thinks about finish and puts a condom on. I've done a test and it's totally negative. Could it of been implantation?