I've completed the main quest, am grandmaster of house hllalu, grandmaster of the morag tong and fighters guild.
What can i do now (my characher isnt cheat enhanced either)

mages guild?

complete the other guilds such as the imperial cult, imperial legion, mage guild, thieves guild (although since you are guildmaster of fighters you won't be able to join them)

free slaves, collect the unique items, complete misc quests, become a vampire etc.

just think of what you could do...such as I made a target for myself...to kill 100 guards, collect every single copy of every book in the game and so on

Start over with a new character. Pick a different race, different class, and different birth sign. Join different guilds this time around. The great replay value of the game is that you can create completely different characters each time out. If you played as a heavily-armored sword-wielding Nord fighter your first time, try playing as an unarmored Breton Magic-User. It will be more challenging than continuing on with the same character (who is probably invincible by this point).