6 days late then period comes only 3 days

I was suppose to have my period on Monday, October 15th. My periods last 6 days normally and I AWALYS get my period when I’m suppose to, Ive never once been late. For the 6 days I’m suppose to have my period I never got it (oct. 15-oct.20). Sunday, October 21st came and I started spotting very very lightly, just brown and it was afternoonish. Monday and Tuesday (October 22-23) I bleed heavy, my normal period. Today I stopped bleeding but went back to the brown “blood” discharge. But the thing is it was only “3 days”. Late Sunday, all Monday and Tuesday, and only half a day today...when I had the missed period I was nauseous (still am a bit) I couldn’t really eat anything (not like me at all), I peed a lot, i have been extremely tired and kinda feel weak, I have a lot of the pregnancy systems and i also feel different. Can I still be pregnant. If so when she I take a test? I heard 3-4 days after the “IB” if this is what it could ??? I’m so confused. Yes I took a test last Wednesday and Saturday, it was BFN I was super bummed out. Me and my fiancé have been TTC for a while now. Then my “period” was extra short which also never happens. I’m wondering if this has happened to anyone. Or if anyone things im pregnant and when I should take a test, help please.