Spotting - What Does it Mean?

I'm 26 and have been TTC for five months. I have an abnormal cycle that can last up to 49 days. My period isn't predicted to be due for about another 18 days and I'm currently ovulating, according to Glow. 
I woke up this morning to spotting when I went to the bathroom. I have never experienced this before and I'm wondering what it could indicate. Any thoughts would be greatly appreciated. 
Thank you! 

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