Dude...I can relate a lot. We are really, really similar!
First off, huge respect for coming to terms with alcohol. I always had a problem abusing alcohol ever since I started drinking as a 13 year old. I battled myself for many, many years about how much I drank, how often I drank, and all of the associated feelings of guilt and shame and anger and everything. I tried moderating and switching what I drank, trying to set rules for myself, everything, and I continued to drink way too much. Even though it hadn't cost me anything like my marriage or job or drivers license, it was still an issue.
About five years ago I quit drinking. It took a couple times to make it stick, but I quit cold turkey and haven't looked back. I'm very glad that is in my rear view mirror now. There's really no upside or benefit at least for me in drinking. What helped was the Reddit r/stopdrinking and the book "This Naked Mind" which explains everything about alcohol addiction and how to reverse it.
One thing I found is that for me at least (and I know a lot of others too), I was not able to moderate drinking after quitting for a while. I quit for several months and then had a beer, within a week I was right back to my usually 4-6 drinks a day and sometimes more. Quitting completely made the decision super easy (I just don't drink).
So, everything else. I just turned 40 a couple months ago, and physically I've felt like crap a lot like you are describing.
I used to go to sleep somewhere between 11pm to midnight and then wake up at 6am. Even with little kids that I had to get up with through the night, that was fine. But starting late last year, I would get tired at around 8pm and sometimes go to bed and sleep until 6am. I would be exhausted a lot of the time and then just lay down and sleep. Even yesterday, I fell asleep at about 7pm for 30 minutes for no reason. A lot of nights I used to stay up and play guitar, but much of the time I have no energy and just go lay in bed after the kids go to sleep and I'm out within 15 minutes.
I've always been overweight, but that weight keeps creeping on. When I hit 10 years old, I went from skinny to chubby, and got up to 185 pounds at 5'6" in high school. In college I cleaned up my diet a lot and went on supplements and got down to 135 pounds (skinny but no muscle). Over the years that crept up to 150, then 165, then 190, then 200, and now up to 215. I've got more muscle than I did when I was young but I'm easily 50-60 pounds overfat. A few times in my 20's and early 30's I could lose up to 25 pounds by dieting, but I haven't lost any real weight in close to a decade even though I constantly watch what I eat and try different diets. And now I'm starting to get those nagging pains. A lot of lower back pain, pain in my knees especially going up and down stairs, etc.
While I don't exercise in a gym, I play hockey 1-2 nights per week and have for over 15 years. My ability to perform on the ice has greatly diminished the last couple of years. I was never very good, but I've definitely gotten a lot worse. Our league rates players to make sure you're playing at the right level...I was rated a 3.0 or just a bit higher a few years ago, which is kind of an average adult player (1 means you have no idea how to skate or play at all, 5 means you are former pro or D1 college). That slipped to a 2.9, 2.8, 2.7, and now like a 2.6. I can't skate as fast, don't have the endurance, and because I'm tired on the ice my overall game is a lot worse. I had to drop from the medium pace league to a slower/older level which was depressing.
Last thing, I've battled anxiety issues most of my life. Sometimes I have to use medication for it to back it off, sometimes it doesn't bother me for months at a time. I would say now it's okay, but there's been a few times where I basically stopped eating and functioning because it was so bad. CBT and mindfulness helped me to manage it for the most part, but I do need meds sometimes.
Now, pulling this all back to Covid. I don't know. I had Covid twice...first time was early 2021 where my whole family got it and we all had a mild cold basically for a couple days. Second time was fall of last year and that hit me harder, but wasn't devastating by any stretch. My fatigue got a lot worse late last year, but not sure if it's related or not. I never had the really bad symptoms, and haven't been sick at all for many months.
I really don't know what the solution is. A lot of it looks like "aging" on the surface, but I know a lot of people and most of them don't just fall off a cliff in terms of quality of life at the age of 40. I've been watching some videos on people eating a carnivore diet the last couple days and think I may give that a shot. I've done just about everything else and I'm so sick of struggling with food like I have for 25 years. A lot of people describe similar problems where it seems their health is just going to hell at a relatively young age and they just said "fuck it" and ate like two steaks a day and lost 100 pounds in a year and felt great and no longer even think about food.
I just got a Costco membership and I think I'm going to get some roasts and other meats and try it for a couple weeks. All I know is I just turned 40 and I don't want to just feel more and more like crap every single year until I die. If it ain't broke, don't fix it. And if it is broke, do something different. Right?