When you say drink a lot, do you mean 'neck a pint'?
I have to say the only time i got pain from drinking was when i forgot and gulped it down. If you are sipping away at it rather than big mouthfuls you shouldn't get pain.
Fluid is straight through (especially at your early stage as there is no solids in there to slow the progress of it) in one end and out the other...
Don't worry if you are drinking a lot. That is a FANTASTIC thing to do, fluids are the most important thing for you right now...
If you got any worries, feel free to message me xx