What does the moodlet say? Doesn't it tell you what is causing it? The only time I get that is when I put in the cheapest or used furniture and my Sims get an uncomfortable moodlet after using the objects. There is a very cheap shower and a bed that has an uncomfortable effect, but there is a similar item that don't have it. It says "uncomfortable" in the item description. Check your beds, showers, sinks, stoves and ovens.
I really like this feature lol. My University students or unemployed Sims get all the cheap, used furniture and are always uncomfortable until they gain enough mechanical skill to upgrade the items or can buy a better model, but there are only a few objects that do this actually. I think we got a few uncomfortable, used furniture with the University pack.
