Can’t tell

So this morning I woke up with a little dark brown blood in my panties but I’m not supposed to start my cycle until Wednesday/Thursday. I didn’t cramp or anything like I usually do before my period. I was nauseous and had a terrible headache last night but that’s it. but if I continue to bleed I would have started my period two days early but I don’t have my usual period symptoms. Could it be implantation bleeding or did I just start early?

Tested last night and just now and both came out negative.