Advice on my 7 week old?

You might try smaller, more frequent feedings. Are you feeding her on a schedule, or is the every 3-4 hours her idea? If the former, feed her when she shows signs of hunger, and don't worry if she seems to need to eat more (or more often) sometimes. Young babies have frequent growth spurts, and need more on some days than others. Spitting up isn't necessarily a problem, unless she seems to be in pain. Water isn't a good idea.