I have recently lost another follower. I went back to where I was with them but nowhere to be seen! I go and try to rehire someone but they're saying I have someone with me. how can I fix this without having to go back?

I have done a lot since then and I don't want to lose anything that I have done!

Have you tried fast travelling back to where you recruited them?

This has usually worked for me (on XBox) but, it has to be fast travelling, not just walking back.

Which follower did you have?

Wait at least 3 days. They should return to the location you first hired or took them onboard.

They are hiding from you because they are sick of fighting dragons and dungeon diving

I had one from the Dark brotherhood.

What are you playing on ... PC, 360 or PS3?

Then go back to the DB base, and that person should be there. They will go to whatever their home base is (Lydia goes to your house/Dragon reach if you haven't purchased the house, Erandur returns to the shrine of Mara he set up in the ruins, etc.). If he/she isn't there, wait a few days and they should show up.

Same thing has happen to me. I play on Xbox 360 and it seems nothing helps. I have waited 30 days. She is trapped in Markarth and will not die or leave. My follower is a Dark Brotherhood Initiate. I went back to the Dawnstar Sanctuary and she never returned. I have also cleared my cache on my Xbox as informed by Bethesda Technical Support.

try to wait 3 days: followers automatically leaves and return to where you hired them if they are in wait here command.
If not its a bad glitch it happened to me sometimes thats annoying youre stuck and cant hire someone else....