Spotting a week before my period and now 3days late on period. could the spotting been my period even though my periods are regular and heavy?

No spotting was too : Soon, please make sure you are not pregnant, and if u do not get in your period in a few days then see your gyn for evaluation.

Yes: It's possible that there was some variation in your cycle this month. I would want you to take a pregnancy test as well. If periods are usually normal, then likely a hormonal variation. If continues you may want to talk to md about birth control to help regulate cycle. Hope that answers your question, be well.