Ladies experienced with this stuff?? Thoughts?

AF is usually due regularly the 4th of every month, well this month March it came the 5 but I BD all fertile window plus the days right when AF ended well today I've experience darkish brownish pink CM then followed by light pink spotting my AF isn't due again until 4/4-5 also having some lower abdominal & back cramps not noticeable though. Can someone explain what's happening?? I have been TTC for about 6 Cycles now!!