Impantation bleeding or AF?

AF is due 29/07, yesterday after wiping noticed brown tinged cm. Did a cm check and there was some more darker brown cm. Did another cm check today and cm is slightly brown but not as much as yesterday. Having on and off cramps today I think it's mainly on the right but not sure. Don't have any other symptoms other than tender nipples but that's normal for me before AF. Don't remember having brown cm before AF before.