My senior dog for the last day or two is licking his lips non stop. It's so bad that it even woke me up several times from my sleep last night. He's not licking his nose, it's literally just his lips. And he makes such a loud noise while doing so. Anyone have any idea why he could be doing this? His teeth aren't in the best shape (shelter dog adopted as a senior so it's a lifetime of poor hygiene I'm battling) but I brush them at least once a week (he really fights me) and he's had the really bad teeth removed.

% sorry didn't notice my phone autocorrected licking to locking. We have a 3l bowl for them that we fill and change fresh water for them daily, sometimes twice daily if it's a particularly hot day, but I'll definitely try get him some electrolytes. He eats and drinks perfectly fine, gets treats and has no problems eating even hard biscuits despite some of his teeth being in poor shape. His gums did bleed the first few times I brushed them but they didn't last time, I'm also spraying colloidal silver in his mouth too in case.