AF irregular

Shani
Since my misscarrige in January I've had 3 periods. First was 6 weeks after the misscarrige, second I was 2 weeks late!! Then the third I was dead on time. I was due AF 4 days ago and still no sign tested and got a bfn!! 
Why is my body doing this to me?! We have been trying for almost 6 months and we're still not pregnant..
Could there be something wrong?