Just because you see spotting, it does not mean implantation has happened. It could be the first day of your period or some other medical issues. The way to know the difference is to know your body before implantation. To do this, you must track your normal menstrual cycles and pay attention to how they start.
Some women start their periods heavy while others spot first. Some women have cramping days before, some have it only after they start their period. Know your body and how it normally responds to you monthly. If it does not feel like your menstrual cycle and you have had unprotected sex, pay attention not only to the heaviness of spotting, but also to its duration.
If you feel it is implantation and do not want to wait until your period to know for sure, you may take a home pregnancy test. However, remember that first implantation happens and you become pregnant only after the proper egg embedment, so the HPT may not be accurate. Try to take your first morning urine for testing, because the HCG level in such a case will be higher.