Is there a way to play after the credits ? it brings me back to the main menu and i can only go to my game just before the end

Sorry friend it's just like Fallout 3. Were going to need to wait for the dlc to be able to continue after the credits. Just play around and do other things before the last story mission, that's what I'm doing.

Mods, maybe. If there is one.

Otherwise no. Maybe a DLC will add it in the future (like with FO3).

The game gives a dialogue option when entering the final chapter telling you explicitly it's the point of no return, so you can do the MQ up to that point and simply not go to the final area until you're ready; or not at all, if you're so inclined.

Don't [censored] on a continuation DLC though. Mr. Sawyer was pretty adamant that he and his crew wanted the story to end. And it's not really a big deal. Load a save and continue on.