Belligerent dachshund barking

Hi I have a now 12 week old mini dachshund who has recently begun barking incessantly. We had an initial rough few days transitioning home but since then he’d been great. Pretty much fully potty trained maybe 1-2 accidents a week and that’s on me for not paying attention.He was sleeping in his crate and would even go in there on his own when he was tired. Loved his play pen and all of his toys. We had a pretty strict schedule of 30-45 min wake windows consisting of potty, play/ train, then some sort of chew enrichment activity then back to bed for 1-2 hrs repeat all day until night time. He was doing great and loved the structure. A few days ago he was acting funny scratching at his ears I took him to the vet and he had a double ear infection. Got him treatment but for those few days he was so whiny and only wanted to sleep on my chest nose buried in my neck and anytime I’d try to put him in his bed hysterical sobs and barking. So the schedule really went out the window because of this and we did no training outside of potty and crate at night time. He’s now doing better back to playing and enjoying activities however the crying and barking hasn’t stopped. Putting him to bed is genuinely a test of wills who will givein first me or him. I have changed nothing about his crate setup. I have it covered, litter blanket, old tshirt of mine, white noise, near me etc. and he loved it before this. I do the whole routine of giving him a settle command he settles I take him out to potty he does or doesn’t we go right back to the crate and say bedtime the close the door. He might settle for a minute then immediately is screaming barking you’d think he was being chased by an ax murderer. He’s now been barking during the day the second I’m out of sight. Which he hadn’t done since the first few days home. I feel like we back slid so much and I’m worried he’s forming bad habits despite all of what I’m trying to do. I have tried to pet corrector like air that makes a hissing noise and I swear it just makes him more crazy it’s like any attention riles him up and gives him more fuel. Feel so bad for my neighbors because I am in an apartment so my night time anxiety has been so high. I pretty much cry all night he does eventually tire out and go to sleep but it could be 30 minutes or more of him screaming. Typically he wakes up 1/2 times a night and the whole process starts over of him screaming etc. I know dogs bark and especially dachshunds. So it’s unrealistic to expect him not to bark. How can I best get this under control now before it’s true habit. He doesn’t bark at anything outside he’s been to plenty of coffee shops etc. we live in a big city and has been great around that sort of stuff. I feel myself getting very frustrated with him and I have been having to put my AirPods in and just try and regulate myself with how overwhelming his bark is. I work in a hospital and eventually will have to go back to work and he’ll have to be home for a few hours at a time. I’m just worried he’s formed bad habits now because of me. Any and all suggestions would be helpful. He is extremely food motivated and was doing great with the basic training we did the first 2 weeks. I just feel slightly helpless I love him so much but I’m at a breaking point.