How can I improve playing Trundle in top lane?

I have tried to go Trundle top but I am having issues against heavy pokers such as Irelia, Olaf and Darius. I start with boots + 3 Health potions and then building Wriggle's Lantern and Hexdrinker, depending on the enemy team. I then follow up with Trinity Force. But in the laning phase, it is very difficult to sustain and to win the lane. How do you win the lane as easy as possible as Trundle, the almighty troll?

You said you started with boots+3.

When playing versus heavy harassers, so like you mentioned, Irelia, Olaf, Darius etc., Cloth Armor + 5 pots will probably be a better start as you will sustain through the damage and will still use the item to build into Ninja Tabi/Wriggle's Lantern/other armor item later. That different starting item should ease you through the earlier levels so you manage to pick up some sustain.

With that in mind, versus the champions you mentioned, Trundle will have a hard time sustaining simply due to the level of harassment those champs can put out, as few champions can stand up to them.

I'd also argue that Frozen Mallet is a better buy on trundle than Trinity Force, simply because he has no heavy gapclosers and will need the slow to hang onto enemies. That's just my two cents. I'm not a huge Trundle player.

Irelia, Olaf, and Darius are all strong tops, Trundle is rarely played at all and when he is is traditionally played in the jungle. That being said, Trundle is less of a duelist than champions like Olaf or Irelia, and your main focus when getting beaten might have to be surviving lane phase until you can team fight effectively. If you are getting pushed around in lane and your jungle is unhelpful, sometimes you just have to keep buying defensive items and surviving. That being said, jungle ganks are always going to be helpful and if you keep losing repeatedly you may want to start Cloth Armor and 5 pots, especially if you are going into Wriggle's Lantern later.