Don't say "gain weight", say "add fat". You can gain weight from drinking water and retaining it.

If you burn more calories each day than you take it, you will have to burn fat. That's just a simple fact of physics.

I can't answer your question about "stay within my calories intake" because that statement makes no sense. Everyone stays within their calories intake because it's their calorie intake. If they eat more or less, it is still their calorie intake.

Good questions get better answers.

Good luck and good health!!

♠