I've been dehydrated, increased urination, and feel way too hot since starting beta blockers. can't retain any fluids, and will get faint if not guzzling water/gatorade. what does this sound like?

Maybe diabetes: B"sd first ? is why are you taking beta blockers. Polyuria is rarely seen only 0.1773% of patients report it. However, one possibility is unmasking of diabetes by beta blockers - "β-blockers are thought to contribute to the development of hyperglycemia by impairing the release of insulin from the pancreatic β-cell." So a good start is to check your blood sugar on the nearest glucometer!

Talk to your doctor: Theoretically speaking, beta blockers, by inhibiting sympathetic functions, could cause unopposed parasympathetic functions. Talk to your doctor about a trial of stopping it a few days to see if symptoms resolve. However, maybe you have another problem unrelated to beta blocker. Have you been checked for diabetes?