So early on in the game Lydia started following me. After a few times of her dying and reloading I started telling her to wait for me either just outside the area I was expecting to battle in, or back at town before setting off for a guest. Well, I left her waiting in the Companion's building in Whiterun before a quest, during the quest finally acquired my 5000 gold, bought Breezehome before heading back to the Companion's building to pick up Lydia, and found her to be gone. Found her in Breezehome when I went there to drop off some stuff. Told her to start following me again, but she insists that I've already got someone following me and won't join my party. I thought it might be just Lydia, but in coming across mercs for hire and other possible followers, they all give me the same message when I try to get them to join my party. At the moment, the only person I can get to come along with me is the dog in Markath.

onmund is broken for me he never helps in a fight i think it might be related to the frame rate issues but at some point he decided he doesnt want to help

Cut their heads off and forget about them.

I've been kind of wondering if sacrificing Lydia would reset my follower bit and allow me to get other people to follow me. I haven't tested it yet as the character I'm playing is trying to stay on the good side of things.

My Farkus disappeared on me yesterday and hasn't returned. I am getting the same "looks like you already have someone" message from other followers but I can't find Farkus anywhere. It has been a total of about 50 in game hours without his return so I am starting to get a little nervous. I pretty much only use the followers as pack mules but it really helps me stay out of town longer since they can carry a lot of loot. If I can't get another follower, I'm going to have to start leaving a lot of loot behind or visit towns more often to store and sell it.

The best follower in my opinion is the summoned assassin. You don't have to feel bad when it dies, if it gets in the way while the steel is swinging and the magic is flying.

i've noticed that the further I've gotten in the game, the more Lydia doesn't follow me as well as she should. She sometimes just stays near a tree or something, and I have to go to her, sometimes several times, before she starts to follow again. She's disappeared a lot, even for such long periods that I end up thinking she died "somewhere" in battle, only to find her RIGHT BEFORE reloading a previous save game. It's gotten to the point where I really don't need her for anything other than to hold the extra belongings I can't carry.

Since I'm a two handed fighter, she gets in the way and gets killed pretty often, forcing me to reload.

I figured out what was wrong with my Lydia ...

After telling Lydia to wait for me I had apparently started the Proving Honor quest with the Companions. When Farkas went to met me at Dustman's Cairn he counted as my Follower the whole time. Once I completed that quest with him and he came back to the city I was again able to hire another Follower. Unfortunately I had already killed Lydia to see if doing so would free up a the Follower spot, but that didn't work.

I thought the same as the OP at first till I realized I had a quest open that a NPC was to meet me somehwere. Come to find out that is why Lydia and other npc's wouldn't join me. You have to make sure you finish the quest in Whiterun I believe it's the Companion quest which i forgot the name of. **Spoiler** It's the werewolf quest. This will fix npc joining you.