Hi Arundinaria, I have some fluid retention from my blood pressure medications. On the days or weeks that I have to increase the dosage I can go for a month or more with an extra 20-25 pounds easy. Lasix isnt an option for me as I have really low blood pressure problems...but anyway. 
With the itching thing, you are going to need to factor in that your body isnt getting rid of your fluids properly, which in turn means that you will need to step it up with keeping hydrated. Itching can be a sign of your holding onto too much sodium which your doc can run labs for or by being dehydrated and your body not functioning properly at times a lot of people who tend to retain fluids such as this will have dry skin.