Gaining weight

Do you weigh/measure all your food? Exercise can cause you to retain water, which can hide fat loss on the scale. Don't stop, it's good for you, just know you might not see your fat loss on the scale for a couple weeks

3 weeks isn't long enough to gauge what a certain calorie amount is doing. Give it a few more weeks. If no loss then you're taking in too many weekly calories.

If in fact you are taking in a true 1,600 every day of every week and not losing and working out 6 days a week you may be holding water. The symptoms are shown if you have bloating in your midsection especially.

you didn't mention your height and weight so that would be good for you to post for accurate answers.

You haven't given us the information we'd need to assess how realistic 1600 is as a goal for you, like demographics and activity level. Your MFP profile says you're female, and 1600 would be a calorie deficit for lots of us women, but not all of us; and it might be a small one for some. Nothing wrong with a small deficit for slow loss - quite the contrary - but realistically it would take longer to show up on the scale amidst normal, multi-pound/kilo water and waste fluctuations that routinely happen from one day to the next.

For sure, in 3 weeks you've - sadly - not gained enough new muscle to outpace any realistically satisfying rate of fat loss, no matter the exercise. I wish it were otherwise, but muscle mass gain is a gradual process under the best of circumstances, and lowered calories aren't the best of circumstances, so it'd be even slower.

I agree with others that 3 weeks isn't long enough, and that new exercise often adds a surprising amount of water weight almost instantly. If that's what's going on for you, then hang in there on this routine, because the water retention will balance out as you adapt to the exercise schedule, and as slower fat loss starts to show up from behind the mask of any remaining water retention. Sadly, it takes patience and persistence.

The common advice here would be to average 4-6 weeks of weight changes to see a reasonable estimate of average weekly fat loss. If you're a woman who has menstrual cycles, compare body weight at the same relative point in at least 2 different cycles. Hormonal water retention can be that major. It's not the common pattern, but a few women here report only seeing a new low weight once a month, at a particular point in their cycle.

One thing about that 6 days a week of exercise: If that's all new, I'd advise caution. Maybe this isn't you, but it's common here to see people adopt some punitively intense or long daily exercise routine, to the point of invoking fatigue. That's counter-productive for calorie burn AND for fitness improvement.

Simplistically put, over-exercise makes us drag through the rest of our day(s), so we burn fewer calories doing daily life stuff, effectively cancelling out some of the exercise calories. It can be subtle, but since nearly all of us burn more calories in daily life (job, chores, etc.) than via exercise, it can have a meaningful impact.

On the fitness front, over-exercise implies under-recovery. Recovery is where the magic - the body rebuilding better - happens. Under-recovery slows fitness improvement progress.

Generally, gradually increasing total exercise load is a better route: I'm talking about the totality of exercise type(s), frequency, duration, intensity. A common rule of thumb is no more than about 10% increase per week. The sweet spot is a total exercise load that leaves us feeling energized, not exhausted, for the rest of the day - a manageable challenge. (A few minutes of "whew" right after the workout is OK.) It should also allow good life balance - enough time and energy for all the other important things in life. When a particular exercise schedule starts feeling easy, that's the time to increase one of the variables to keep a little challenge in the picture. The "manageable" part avoids over-fatigue, the "challenge" part creates fitness progress.

Overall, I'd advise what most others have: Give a new regimen enough time for start-up water weight weirdness to be out of the picture.

If your food logging could be tightened up without feeling obsessive, that would be a good focus in the short run. Accurate counting is a somewhat subtle skill, and we all go through a learning curve with it, usually with some "uh oh" realizations along the way. Be sure to log every bite, lick, taste, beverage, condiment, cooking oil, cheat meal/day, or off-plan oopsie. Be sure to select specific and accurate entries from the food database. Being as accurate as practical helps improve weight management predictability.

This process can work for you, but it will take that patient persistence for best results. Hang in there, keep learning, keep improving your plan (easier > faster), and you can do this. The rewards from success are IME worth that effort.

Wishing you success!

you don't gain muscle that fast.