Late implantation Bleeding

Would be grateful for any advice. 36 yr old TTC baby no 1. Currently CD33 and 15-16DPO. Cycle ranges from 32 to 36 days. pregnancy symptoms for a week including, painful breasts, some nausea - tests inc 'first response' all neg so far. Today I spotted with a coral red/pink watery colour.. It's was only on wiping and subsequent trips to the bathroom gave no spotting. Could this be a late implantation bleed?  If so, how could I have pregnancy symptoms before implantation??