Cramping a week before period what's up with that?

Before ttc my periods were regular and super predictable. 28 days on the dot and I knew it was coming because I would cramp only the night before AF and wake up to AF.  Its been that way  six months prior to ttc and since going off bc.  I have been ttc 3 cycles with #2  and since then my period are so off. I experience cramping  several nights  about a week  before AF  but no AF. And when she does show up its irregular days like  24 days, 26 and 29.  Does anyone else experience this since ttc?