pain when drinking protein shakes post op

Hi everyone! I was just banded last week and everything has been going well so far until day 4 when I am now experiencing problems drinking the protein shakes I was on pre-op. After even a few ounces I feel so full I could explode, get sharp pain in my chest over the upper incision point (heartburn?). I have not had this problem with other clear liquids thus far, even jello or popsicles. When I feel this pain I also feel it intensify if I breathe deeply. I am making them with milk, could it just be that I'm not ready for this yet or something else. I am now having to take mylanta for the heartburn pain which I have never had before in my life. I havent even been taking the percocets for the last two days because there is only mild pain otherwise, but this is stronger. Anyone out there have a similar problem so soon post op? Should I wait it out and continue the meds for a few more days?