So I was playing Fallout 3 with Clover as my follower, and I decided to go to Point Lookout, so I had to send her back to Paradise Falls, nothing unusual.
I beat Point Lookout and decide to come back to the wasteland and rehire Clover, except she won't join, saying I already have a follower. Except I have no follower.
I have the same problem with every other follower.

Any idea or console command to solve this problem ?

This is why they added a Companion Terminal to New Vegas.

You can try recruiting Dogmeat, then killing him. That should free up a slot so you can hire another follower. You can ressurect Dogmeat, hire him again, then kill him again to get multiple followers.