AF is no where to be found...

Hi girlies! So I am 4 days late on my cycle (supposed to start Dec.30) I have had no PMS symptoms and no pregnancy symptoms besides twinge cramps that come and go. I took a test earlier today and it was negative (thought I saw a second line but pretty sure that’s my head messing with me) I haven’t taken the pill all month and there’s no signs of an impending period (no sore breasts, no PMS cramps, no acne, no mood swings) Has this happened to anyone before? Did I test too early? Idk what’s going on.