Hi there! First point I'd like to clarify is when you say "soup" are you referring to broth? At 5 days post op, you should not be having soups yet. Only clears and possibly a drinkable yogurt. Now that that question has been posed, I will give you a few suggestions.
You are early out from your surgery. You have swelling and the backed up feeling or full sensation you are talking about is due to drinking to fast. Sip, sip, sip. I would recommend that you slow down. It sounds to me like you are filling your pouch/stoma and it is backing up into your throat. You do not want to do that to your esophogus. The espphogus is a tube of passage, it is not meant to be stretched. It is not made of the same elastic tissue your stoma or stomach is made from. That tissue is made to expand and contract, your esophogus is not.
So, to regroup, slow down your drinking. Sip, sip, sip! This is the time to pay close attention to your body and begin learning the signs of your "new & improved system."
When you feel full, stop drinking....even if you are not finished. Count it as a blessing, your portions are smaller. The more your healing takes place the more the swelling will go down. It is important to not put undue pressure on the band. It needs to heal and scar into place. (it is stitched into place, but those stitches are meant to hold the band so it can scar into place.)
Take it easy, baby steps. You sound like you are doing great! Congrats on being new bandster! Welcome!