Don't worry - you won't break the baby - I promise! I know it's crazy all of the warnings and horror stories that you read out there (and don't even get me started about "What to worry about - er, expect - while you're expecting". I suggest reading "Great Expectations" if you're looking for a good and positive week-by-week pregnancy book).
You can trust your body. Sleeping for example - sleep however you're most comfortable. If your body needs you to roll over, you'll do it without thinking about it. Seriously. The whole left-side thing is NOT something to worry about.
If you're eating a half decent diet you're donig fine. Are you exercising? This can be walking, running, swimming, whatever works for you. The guidelines are to basically keep it at a level where you can easily have a conversation while you're doing it. Don't be scared to exercise.
At this point in your pregnancy EVERY LITTLE PART of your baby has basically already formed. It's just growing now. Check out the amazing photographs at http://www.i-am-pregnant.com/pregnancy/calendar/week/20 - they're truly inspiring. My point is, it's pretty hard to screw up right now. Don't worry about weight gain - your body will take care of itself if you eat good food when you're hungry. And seriously, drink the tap water. What do you think is in there that's going to hurt you?
Here's a reassuring statistic for you: after they detect a fetal heartbeat by doppler (which they certainly have for you) you have a greater than 98% chance of having a healthy baby at term.
Personally, if I were you I would focus on preparing for the birth of your baby. Pick up a copy of "Ina Mays Guide to Childbirth" by Ina May Gaskin and read it cover to cover. Take a childbirth class with your husband so that you both know what to expect. (And don't bother with one of those crappy hospital classes - take a REAL class). Practice relaxation techniques, etc. You want to mentally and physically prepare to birth your baby peacefully into the world. Your body is smart and amazing - it's making a PERSON and don't worry about it - it knows exactly what to do.