At some point in your second trimester, you'll probably notice that sleep doesn't come to you as easily as it used to. Popping in and out of bed to go to the bathroom doesn't help. Neither does the fact that it's somewhere between difficult and impossible to get comfortable at night.
There is very little you can do about the reduced capacity of your bladder that doesn't involve dehydration and suffering of another sort, but there is one simple thing you can do to help yourself get comfortable in bed, and it will cost you relatively little. Go to a bed and bath store, or pick up a catalog that sells bedding, and you'll probably find a body pillow. Body pillows are long, skinny pillows filled with down, or cotton, or any number of less expensive synthetics. When you get into bed at night, position your body pillow in between your breasts, around your stomach, and in between your thighs. This will give your body the support it needs, and will finally allow all of your muscles to relax.
When looking for a body pillow, know that there should be one within every price range, and that you will regret anything but a washable cover. Know too, that with your body pillow in place, your significant other may become lonely and jealous, so make sure to pay attention!