What causes late AF??

Melissa • I`m a newlywed who just got married August 23, 2014. My hubby and I have officially been together for 4 years and are trying for our rainbow baby. We lost our first at 8 weeks in December. <3

AF is never ever late for me...today I'm a day late. 3 pregnancy tests and all negative. Same symptoms I had when I was pregnant before (exhauated, hungry, sore breasts and nipples, dull cramping that's been going on for 3 days). But the tests are negative...I don't get it.

I had a D&C for my mmc in December and my periods went right back to normal in January and February. AF was 4 days early in march and now already a day late in april. We're TTC and BDing in my fertile window...this was supposed to be our month.

I'm confused, sad, angry and I don't know what's going on. I'm trying to be positive about it but I'm afraid I'm not ovulating or something anymore now that I had the d&c.