Delayed period, negative PT result. Opinion please?

Ena

I am now 4weeks delayed from my period. My last period was Nov 23. On the 24th of Nov, we had sex and we didn’t pull out. I think, we are safe on that day. I had a spotting last dec 17-20. Since then, my period hasn’t come yet. I took a PT last Jan 16. It came out negative. Could i be pregnant or just a change of cycle?