Spotting can be pretty normal in between periods- sometimes it's due to a shift in hormones or other factors. It can be due to implantation during pregnancy, but that's pretty rare, and it doesn't sound like that's likely in your case due to the fact that you have always had protected sex. While sex with a condom can still result in pregnant- it's not a high likelihood. You won't always see pregnancy symptoms- and as early as you would be, you wouldn't feel them yet (but again, I doubt you are pregnant).
To be certain, wait about a week and test- but I would lean towards you getting a negative. Let us know how you are doing!