TL;DR: Haven’t exercised in years, every muscle is very sore two days later, what do?

I’m a fat bastard, have been since childhood. I’m pretty fit (for a fat guy). Beginning of the year I’m 6’ even and 280lb. Diabetes runs in my family but I always figured I still had time, until my cousin only three years older than me gets diagnosed type 2.

So I start a keto diet, lost 30 pounds so far (before Thanksgiving and Xmas fucked me a little) and that’s just from diet. Still haven’t exercised at all. Two days ago I sign up for a Y membership, go to their gym, and having no clue what I’m doing, I basically pick a machine, slap on low-medium weight, push to absolute failure, then pick a new machine/muscle group, rinse repeat.

I pushed all the muscles I found machines for to failure, then did them all again a second time, and left. I felt real good about myself that day, but yesterday I was pretty sore all over, and got shit sleep last night because my arms and shoulders are killing me. I don’t think I sprained or pulled or ripped my muscles or anything.

I was going to work out again today, go every other day. Is every three days more realistic, doing full-body workouts? How do I avoid the soreness, or should I even try to? I don’t mind doing what it takes to get healthy, it’s just really annoying that it’s fucking up my sleep/might affect my work when I go back after the holidays.