Sad???

I'm heartbroken. My baby just turned six months and is SAD. He will be playing and then all of sudden make a poudy lip and then tears...Not like fussing. But crying..???? I'm a sahm. I play with him all day, I hold him for naps. I nurse him on demand. I sing and hug and tickle and love him all day. He also has been like cuddling up to me. Which he never does. Like will just melt in my arms and look longingly at my husband. or the cat. or out the window? What am I doing wrong. Do you think he doesn't like me?? Am I not doing enough, and that makes him sad?? omg. I'm a mess...