Spotting for 4 days? Common?

Hi! I have a question about spotting. My fiance and I have been having unprotected sex for over a year and this cycle decided to get serious about TTC. Opks, Temps, etc. Still difficult as I suffer from very irregular cycles 28-70 days in length, no two months ever the same. This cycle I got my positive opk on CD 16 but started spotting on CD 23. I'm currently on CD 27 and still spotting. Very small amounts, seen maybe once or twice a day. The first day it was very light pink. Then got really dark and stayed that way with just a spec of red. I use fertility tracking apps. Period not expected for another week or two according to the apps. Could I be pregnant or could there be another reason for the spotting? Maybe just a super light period? I plan to take a hpt in a few days but wanted your opinion. I've never dealt with this before.