What could be wrong if you have a little bleeding 15 days before your period but you had a normal period last month?

It could be ovulation, some women have spotting when they ovulate. Or it could be the bleeding of implantation of the fertilized egg which occurs 5-7 days after ovulation. If you stop having any bleeding and have nausea and/or breast tenderness, then you are probably pregnant. If the irregular bleeding persists, see your doctor.