Ok, so I almost finished the main story of Fallout 3, then I bought the add-on pack The pitt and Operaton: Anchorage..
My idea was to finish the story first and the Go out in the wastelands and explore some more and play the add-on pack.
Here′s the problem. After I finish the Fallout 3 game′s main quest everything ends with Ron Pearlmans voice and the credits comes on and then I′m back in the game′s main menu.
So in order to play the add-on pack, I′ll have to load from the save just before I finish the main quest... can′t I just somehow play the add-on packs after Fallout 3′s finished.
..same thing with Broken steel and point lookout this is very annoing

Broken Steel is the only DLC that lets you play after the ending. The rest, you have to load a save.

If you are on Pc, you will also need to make sure that you activate them on the launcher, under the data files option. If on console just make sure they are installed correctly and the game is patched up.