Brown discharge when period is due

Sooo I’m on the pill. I’m pretty good with my pill, I skip my period quite frequently but I do always take it or double up if I forget.

If I do miss a few days I normally get my period. I missed a few days last week, but no period. Instead, I’ve had like a brownish coloured, thick mucus discharge.... just wondering if anyone else has experienced this & if it’s something to be worried about?