Light discharge for 2+ weeks

Jess
I was having very regular and predictable periods for years and in the last year they’ve become less predicable and more sporadic. This month, I started having brown discharge (old blood) that was really light, hardly worth wearing a pad some days, other days there’s just a small amount making it to a pad. This has been occuring for almost 3 weeks now! 😩 In the last 5 days I’ve started having a little bit of red blood mixed in with the darker old blood. Still very little making it to the pad. 
I’m a virgin so I’m definitely not pregnant but wondering at what point I should be concerned about this really abnormal discharge.