So I've had quite a few people to follow me so far, I've had Hancock, Dogmeat, Codsworth, and a few other I think. I most recently have had Cait so I sent all my followers to Sanctuary. I made it back to Sanctuary to have them follow me again and the only one left is Codsworth. PLEASE HELP!!

How long from you dismissed them, to you traveling there? It can sometimes take some time before they arrive (they don't teleport instantly, but have to travel there using ingame time). And I suspect, that some of them, have a bit of mind of their own, so they can go back to where they came from originally. So perhaps look at their original starting point?

Thank you. I now Hancock was my companion before I did a mission for him and he got kinda glitchy.