I can understand that you just be feeling frustrated! The next step would be to calculate your TDEE total daily energy expenditure and then log your calories for each meal to fall under your TDEE, it is important to weigh your food rather than eyeball the servings. You may be consuming more calories than you think and it is the most likely reason you aren’t losing weight even with OMAD.
Prozac isn’t known to cause weight gain, and is considered weight neutral so I don’t think this could be the reason you aren’t losing weight. Some pain medications are affiliated with weight gain, an example being prednisone which causes fluid retention as it causes the body to hold onto sodium. If you are on a similar medication you may see improvements monitoring/lowering your sodium intake.
Similarly eating a diet high in starchy foods can sometimes cause fluid retention as the body is required to use more water molecules to break down the food before it is able to be absorbed (hydrolysis), so reducing your intake of complex carbohydrates (polysaccharides) may result in less fluid retention.
Another method you could try is to extend your fasts to 36-48 hours once or twice a week to see if there is any improvement in weight loss.
I’m wondering about your statement that you can’t exercise at all due to your feet and knee OA. That doesn’t seem healthy to me nor is it going to help you in your weight loss. There are lots of upper body and core exercises you can do that would not involve knees or feet. I would be happy to suggest some if you like, but I’m sure there are tons of resources out there. My old gym had a “bike” that you pedal with your arms as a cardio machine for people who couldn’t use their lower body. There is also water aerobics, which would use feet and knees but is not weight bearing—people I’ve known with arthritis have found it very helpful, though of course your situation could be different.
I feel like someone who stops exercising would invariably have an issue with weight management as their muscle slowly erodes away. Your base calorie burn will keep getting lower and lower the more muscle you lose.
Other comments have suggested insulin resistance or metabolic syndrome which I have along with pcos. I only get results when I eat low carb, high fat (ketogenic) meals. This along with fasting is what is working for me.
Here, this may help you. I talk about sitting in a Jacuzzi for an hour or more (the more you sit in it the more calories you burn). You’re body will be burning calories to keep cooling you down and you can keep drinking water. You’ll find you lost like 3 pounds or more if you sit in it long enough and the benefits keep continuing. You can also do some stretches while you’re in there. https://www.reddit.com/r/intermittentfasting/comments/hoi62q/my_findings_on_fasting_fat_loss_and_muscle/
As other people suggested, get checked for insulin resistance / metabolic syndrome, and learn to count calories. Counting calories is a tedious operation, especially in the beginning, but you can definitely ingest a lot of calories in an hour if you’re not paying attention (healthy food is healthy because it’s rich in nutrients, but it’s not calorie free so you still have to be mindful of the portions).
About the meds: fluoxetine doesn’t make you gain weight as far as I know (I used to take it in the past and I don’t remember reading anything about that in the package leaflet); pain medications might play a role in water retention (but it should be a temporary issue, so after 7-8 months you should still see a weight drop).
I also encourage you to talk with a professional about it. There’s only so much that you can get from a forum..