How can I avoid hurting after exercise but still have the exercise be effective?

Some background if it's needed, I used to work very physically intensive jobs, construction and warehouse labour for the past 4 years. I found out last year that I was born with a connective tissue disorder that I've had my whole life. I found out right around the time that my body started to shut down and I developed exertional compartment syndrome in my legs, and I also discovered that I have a completely torn labrum in my right shoulder that I've had for a long time and dislocating it all the time is not normal. I also learned I have POTs, got tested for it, and am now taking a beta blocker to keep my heart rate down. Got fired in October due to needing to take time off for leg surgery and needing accomodations at work. (Before anyone asks, the way they fired me was to write me up for anything small that I was doing wrong and officially firing me for having the wrong water bottle for their policy, so there was nothing I could do since it wasn't technically being fired for being disabled.)

Since losing my job in October, I have been basically just sitting around the house not doing anything but chores. I got into drinking pretty heavily, gained 40 pounds, lost a significant amount of muscle mass, and am just generally out of shape. Weirdly, I feel physically so much better than I did when I was working, I'm barely ever in pain, and I no longer have to drink or take pain medicine just to fall asleep. I got a second surgery on my other leg for the compartment syndrome during this time also and have mostly recovered.

Now I'm at a point where I want to get in shape. I gained a lot of weight and lost a lot of muscle over the past 6 months. I have cut down the drinking significantly, almost completely aside from once or twice a month rather than daily. Yesterday I decided to go on a walk to just go out and do something. Admittedly I overdid it, I ended up walking for 3 hours on a paved nature trail. But man, being able to walk after hobbling around for so long just felt amazing. I'll never be able to run, but im so grateful to just be able to walk. However, I am incredibly sore now. I know that losing weight will lessen the strain on my legs, but I need to exercise in order to do so. Trouble is, I have no idea how exercise is supposed to feel.

My whole life, exercising has felt like dying, no matter how frequently I did it. Cardio of any kind would get my heart rate to 200 or 220 easily, my lungs would feel on fire, vision would start tunneling and ears ringing every time. Taking the beta blockers helps, it usually only goes up to around 150 or 160 at the highest now. Any weight training keeps me sore for days after, and hurts in the moment to do unless I use a weight so light that it does nothing. Stretching does nothing, I can place my palms flat to the floor without bending my knees and put my legs behind my head and grab my wrists behind my back vertically due to the connective tissue disorder. I've always associated exercise with pain. Since learning that basically my whole body is screwed up, I guess my question is how much pain is normal with exercise? I know that building muscle and staying fit and losing weight are important to feeling good and being healthy, but every time I've been physically active I feel so much worse than when I do nothing. But I miss being strong. I miss being able to lift heavy things. I'm at a point where doing 10 body weight squats gets my legs shaking and I hate it, I used to haul air-conditioners around and sling bins of copper pipe every day.

Does anyone have experience with getting in shape while disabled, or any advice on how much exercise hurts? I only see people say that an exercise shouldn't hurt unless you're doing it wrong, but surely that can't be 100% true. Especially if you are just beginning exercise after a period of being sedentary. If anyone has jumped into exercising after being out of shape your whole life, how long did it take for you to feel normal and not achy? Do you have any tips for avoiding soreness, like would getting more protein help, or are there any tips on how to recognize when you're over doing it rather than going until failure? Thank you in advance, and thank you so much for any advice.

(Also would like to add that I have been to physical therapy, however every location near me seems to be... not that great. Uninvolved physical therapists, very expensive, basically being told to do one exercise then they would walk away to talk to someone else, no feedback when I would ask questions or need help with my form, and when an exercise was painful or didn't work the intended area they would shrug and not have any alternative exercise to do/would just have me do it anyway. Plus they had trouble trying to fix everything in one hour appointments considering its my entire body thats screwed up, not just one joint or limb like every other patient they have.)

TL/DR, went from working physical job to unemployed, disabled, getting surgery, and not moving for 6 months, body is fucked up, exercise hurts, but need to exercise to get healthier and make body less fucked. How much should it hurt, how quickly can I expect it to hurt less, what can I do to have a better chance at hurting less after exercise (especially when stretching doesnt do anything), and how soon do you start seeing results from exercise? One month? Six months? I have no idea.