Implantation bleeding confusion?!

Yasmin
Af is not due for another week and half, but for the past two days I have been spotting ( only when I wipe). The colour is very dark brown not At all like my usual af, also I've had no cramps which I normally suffer with around the time of af. 
​Could this be early af or implantation bleeding?
​Little confused as this month I haven't been religiously ttc due to working nights a lot .