Don't worry, you're normal. One of my earliest pregnancy symptoms was having to pee a lot during the night, and I haven't slept through a single night since without having to go to the bathroom (I'm 31 weeks now.) In the beginning, it has to do with hormone fluctuations and your body is also working harder to flush out excess toxins so your kidneys are producing more urine. For a brief period in early second trimester things often let up a little bit, and then it starts again as your uterus grows heavier and starts to compress your bladder more.
My sister told me that also right after you give birth, for the first few days all you do is pee and that's the excess water weight coming off. I can't wait to be on a less frequent bathroom schedule myself! :)