I Have Been Getting Unusual Discharge. It Is Dark Grey,

I have been getting unusual discharge. It is dark grey, at first I thought it was brown, but it is definitely more grey and it is odourless. I am on birthcontrol, and sexually active. I had my period about two and a half weeks ago. Mild cramping in lower back, and mood swings. I don't know if this is early pregnancy, or if it is spotting. What can you tell me about thick, grey, odourless discharge. I am 20 by the way too. I have looked it up and it seems to only be a sign of early pregnancy but could it be something else? I don't have an STI, itching, infection and like I said it is completely odour free. It is like a small small period. I only see it when I wipe after peeing, and light spotting through the day.