Have you got anyone to talk to? More specifically, someone to whom you can get your worries off your chest and who can be your cheerleader? Also, such a person can be someone to whom you tell what you need to do and who will (gently) hold you accountable for getting things done. Ultimately, you are your own taskmaster, but right now, you need emotional support. Please get some as soon as you can.
And baby steps. Just as an example, I live four flights up in my building. I have gained (for me) a significant amount of weight in the past year and my fitness level has gone down more than I’d like. I decided to start taking the stairs up as part of my overall plan of fitness. My roommate E, who’s also my friend, will ask me at the end of the day if I’ve taken the stairs, if I’ve done my couch to 5K training and so on.
I’ve told myself when I feel winded at the top of the third landing that it doesn’t matter how quickly I get up the stairs, but that I get there. Eventually, I won’t be winded either. It’s literally one step at a time. And you will get there too! Eh, so you don’t do the whole storeroom in one go, you do a corner today. At least that corner’s done, right? Right.
Good luck!