if you just had surgery, it can take several weeks to a few months for your body to equilibrate. please be patient as this will all get better. its likely part of your healing process.
If you just had surgery, your body will want to retain fluid as part of the healing process. Over the next few days to weeks, the water weight should come off.
I think you you ask your surgeon, if you got fat butt augmentation and start loosing weigth, you will loose some butt volume.
Thank you for your question, not using salt or butter while cooking vegetables, chicken or fish will help reduce salt intake. Cooking at home is a great part of the process since, take outs contain a lot of sodium as well.
After your surgery its important to eat healthy for you to recover a lot faster, only after around 3 months or the amount of time that your personal Doctor recommend you can try to loose weight, keeping in mind, that when burning fat, you will also burn the new fat grafted in your buttocks.