Hi. I Had My Last Period On 23 December. I

Hi. I had my last period on 23 December. I had oral sex on 31st December and couldn't have sex because it hurt too much. We used condoms even when we tried. And he didn't cum. So there was only Precum, not cum.

My periods are irregular. I had them on 27 September, 23 October, then 23 December. I also have a BMI of 14.1 which may cause this.

I've had light mustard (light brown) spotting for 7 days since Jan 15. Today, it turned heavier and a darker brown. What could be the cause?