What Causes Delayed Periods?

In December I went thru an iui procedure with injectable meds...it didn't work, as I started my next cycle on cycle day 27. I am now on the next cycle, day 32 and no signs or symptoms of my period. We have no had intercourse yet this cycle. On day 20 of this cycle, I had very creamy white cervical mucus. I have taken two home pregnancy test, both negative. Why would I not have a period?