Just gonna say it.....constipated.

I do not have many symptoms of pregnancy besides cramping and feeling hungry and slightly tired. But the past two days I have been finding it hard to poop. It makes me super nervous because the book says not to strain but sometimes I have to. It makes me feel like I have to sit there forever!! Does anyone else feel like this? I'm pretty sure it's normal.....and yes I've been drinking tons of water!!