Tribulation is serious trouble or suffering — not a bad day, but hardship that goes on and tests you. The word is formal and slightly old-sounding, and it carries a religious echo, because it comes to English mostly through the Bible, where believers are told to expect tribulation in this life. In Christian talk about the end of the world, 'the Tribulation' with a capital T is a specific period of suffering before the end, and you will meet that meaning in films and novels. In ordinary modern English you meet it most often in the fixed phrase 'trials and tribulations' — the trials and tribulations of running a small restaurant — and here something interesting happens: the phrase has softened. People use it half-jokingly for troubles that are real but survivable, so it can mean anything from genuine suffering down to 'the usual headaches'. That is a big gap, and only the sentence around it tells you which one is meant. The word is both countable and uncountable: 'after much tribulation' and 'the tribulations of her early years' are both fine.