discharge and spotting

so for the last couple of months I have had light spotting in my fertile window which is only a new thing but doesn’t really effect me that much. this cycle my fertile window started on 2nd July and I have been ‘spotting’ since then (it is now 10th july) sometimes the discharge is blood that is a light colour but other times it’s a dark brown or light brown. can anyone suggest anything or tell me what might be going on? i’m not on any medication and i am sexually active. i am in year 12 at school and am quite stressed at the moment so i’m not sure if this could be causing it or not. NEED ADVICE ON THE ASAP LOVELIES 💗