Coming back to the bloodwork, you should get a full panel at least 1x/year if not twice a year. I realize not everyone is fortunate enough to do so, but most of the time insurances cover a large portion of it as preventative care. Blood work can show if you’re out of range on items like your test/estrogen levels, thyroid function & many more areas.
If your current doctor doesn’t support that, I’m sorry but that’s not a great doctor. Blood work is important.
It's not going to balance out the kind of fat loss an obese person dieting can be losing but if you were just a little pudgy with a completely sedentary lifestyle/no muscle previously, potentially you were just gaining muscle at a rate you lost fat.
Composition of what you're eating matters; I personally find a low-carb low-calorie diet more sustainable than a high-carb low-calorie diet.
You also won't lose weight if your diet has too few calories. Its counterintuitive, but if you go too low, your body will compensate by dropping metabolism and raising your appetite; bad combo.
Also, you need to consider that you may be gaining muscle and that's offsetting any fat loss.
Sorry if you've heard this all before, I know how tiring it can be to get the same canned advice over and over. I'd be curious to hear your numbers (calorie intake, weight, height)
Also, one last thing, _DO NOT_ trust the calorie estimates from those apps. If I ate as much as fitbit told me to, I'd gain weight _very rapidly_ despite having set the program to make me lose 2 lbs per week. E.g. fitbit wants me to eat 2500(!!) calories today to lose 2 lb per week. In practice I need to eat < 1400 calories to lose ~1 lb per week and <1200 to lose the 2 lbs per week. I'm 6' 210lb.
I'm not one for fads but I may give intermittent fasting a go.
Lifting once a week does little for your muscles if you're in your twenties. It does pretty much nothing once you've reached your forties. (It's still better than doing nothing, but it won't show much in terms of visible change)
And no, exercising once a week won't make your waist shrink. Losing one pound requires a caloric deficit of ~3,500 calories. If you're the average desk-bound adult male, that means eating no more than 1,500-1,700 calories a day to lose a pound/week. (Your deadlifting burns around 500 calories/hour, so if you do an hour a week, that barely influences what you can eat)
Intermittent fasting is a way to get there, but... it's a fad. It can easily lead to eating disorders. I'd look at what you eat, and how healthy it is, first.