Are you on any medications? If so, it could be your medications that are making you sweat so much, not necessarily the liquids.
I'm concerned that you're not getting enough liquid - as I'm sure you know, with low blood pressure, you definitely need to make sure that you're drinking enough - dehydration can make your blood pressure even lower, so it becomes a vicious cycle. Dehydration can also make your heart beat faster, so it's possible that dehydration is playing a huge role in both your blood pressure and POTS problems.
ggreg gave some great advice about staying away from carbonated drinks, but I'd also like to add to stay away from anything containing caffeine. Not only will the caffeine affect your heart rate, but it can also cause sweating.
I would definitely suggest a consult with a GI doc so they can do a few tests to see if they can figure out exactly what's going on, but meanwhile, even though it makes you uncomfortable with the bloating and sweating, it's VERY important that you get enough fluids during the day.
Let us know how you're doing and what you find out.
Often milk will increase the temperature in a person and make them feel warm. As for hot liquids, like coffee or soups, naturally they will make you feel warm. Now, if you are drinking carbonated drinks, like Coca-Cola, then my guess is the bubbles are bloating you up because for some reason you are unable to belch out the air pumped into those drinks! By the way, always drink name brand drinks, sometimes store brands can do a number on your tummy, make it hurt and so forth. Ordinary alka seltzer original will release any gas buildup in your body, which could be caused by sodas. Water should not cause any problems at all, and you should drink some of that all through the day, but less at night or you'll be up peeing all night. You can get flavored waters in case you don't like the taste of plain water.
You MAY have an ulcer in your tummy, and so if alka seltzer original doesn't relieve any of this sweating and bloating symptoms, you should visit a doctor, for sure. He can give you some good medicines to help your ulcer get better and heal up. He can also check to see if the flap between your esophogus and stomach is working right, as well as the flap between the stomach and the common bile dut is working right, where food and liquids go in and out. Could be some abnormality has happened to those openings a doctor can do an ultrasound or scan to see if those are working right. Again, he will have treatment for those.