I'm a level 28 fighter,i have a pretty good high ordinator armour which i got when i went to Mournhold,an awesome enchanted helmet and a great shield.

The problem is that i can't find any good one handed long swords.I still have a Nordic broadsword,which is ok but i have it since i was lvl 5-6 so i guess i should have a better one by now.

What do i do?

enchant it

By level 28 you should have found many swords that are much better. Search in containers which use Leveled Lists with weapons in them. (which are many)
Go to some bandit/smuggler caves and search the containers.

Dwemer ruins, or Daedric ruins are also great places to find weapons. (especially at level 28)

These are just some of your options.

All I can think is that.... you have not been looking hard enough.

Go for some Stahlrim gear. Imo it has the potential to be the best. And you cant really go wrong with Daedric [anything]