I feel like he doesn't want me anymore

We've been together for almost three years.  We have a six month old baby together and three other kids (2 mine and 1 his).  I've been a stay at home mom since our baby was born.  Lately I feel like he doesn't want me anymore and I feel extremely unappreciated at times.  I take care of the house and kids, cooking, cleaning, etc....sometimes I feel more like his mother than his woman.  We all went to our state fair together last weekend.  I can't help but notice that he practically breaks his neck to check out other girls.  I'm not talking about a glance like I think we all do, but he would physically turn around to keep looking as they were walking by.  I didn't feel angry but mostly sad and insecure about it.  He rarely tells me that I look beautiful like he used to and rarely initiates sex.  Our first year together we couldn't get enough of each other.  Of course things are different now since we have a new addition to our family...I'm working on getting my body back in shape as well.  I just don't know what to do.  I love him and I think he loves me but I feel very lonely and depressed.  I don't want to start an argument about it either because I feel like that makes me look very insecure and unattractive.  I guess we do have communication issues or maybe I'm just the problem.  I don't know:(