Thanks for the query.
As your periods are regular and you had intercourse during the safe period there is less chance for pregnancy
The delay in periods could be due to many causes like hormonal
imbalance, Poly cystic ovary disease, dietary changes, recent illness, thyroid
The spotting you had could be scanty flow representing the periods.
You once consult gynecologist and get examined to find out the possible cause and take treatment accordingly.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429