4, it was probably a cultural runaway, I ended up abandoning the game in annoyance.
How many cities do you have may I ask?
If you are -18 you might have too many cities too make Freedom Viable - an ideology unhappiness hits you really hard if you have a lot of cities. The Freedom policies are generally the hardest to get happiness on. You need a lot of buildings that are generally not that easy to get or are plain bad (i.e. watermills, hospitals, medical labs, mints & stock exchanges...).
You also need a lot of specialists to overcome that -18 hit (that would 36 specialists in total I think). I suspect one of the culture runaways probably has Sacred Sites (at this point you are probably better switching ideology), unless you think you can build a lot of happiness buildings quickly. If you haven't built colosseums and zoo's you might have a shot at fixing things - but its going to slow your game down considerably.
You're best bet might be to try and ally some mercentile citysates - you can get +10 happiness from one citystate alliance.
If you rushed Radio and the Eiffel Tower is still available you might be able to grab that with an engineer and pump out great musicians to try and get to 10% tourism over your neighbors...