Cycle after baby

So I finally got my period back this past November. My daughter is 16 months and I quit breast feeding this past October.

My first period in November lasted 7 days. Tad longer than usual but not too bad. Well based off of that my app suggests my next period should have been December 10th, but it hasn’t shown up yet. I’m now 18 days late for my projected period. I took a home pregnancy test on December 19th and it was negative, then over Christmas I started feeling nauseous and getting headaches and had a bit of spotting yesterday but still no period. Should I test again?

How long did it take for your cycle to return to normal?

I was always regular before, never being more than 2-3 days late.