Querulous means “having a tendency to complain” or, more directly put, “whiny.” Sure, no one can be happy all the time, but that’s no excuse for being querulous.
Querulous may remind you of the word query, which means “question.” However, the two words are not closely related. It’s perfectly reasonable to make a query; just don’t be querulous if you don’t like the answer you get. Querulous does share its origins with the word quarrel, which means “argument” — and that’s what’s likely to happen if you complain too much.