Why am I so mean to my boyfriend?

My boyfriend and I have just had a baby (18 days ago) and I have found that I am still being a witch to him occasionally. He is a great dad! He helps take care of my son from a previous relationship. He works and lets me stay home with the kids. He never looks at other women even though I do. He just isn't that great with the relationship thing. We have a less than desirable life. He is VERY unromantic. He has no sense of humor. I feel like it is very boring to be with him. Also, now that I am trying to get thinner after having the baby, I feel like maybe he should lose some weight as well (he is overweight). So sometimes I am kinda mean to him about things. Like I guess kinda naggy. I have never been the nagging type and I love him. Are there any other women who think they would have the perfect guy if he just had a better personality? Am I being to mean by thinking so harshly about him? Will this go away when the pregnancy hormones are gone, because I have gotten a lot nicer and I have enjoyed him more (not ually) since the baby has been born. Thank you!