Im 5’2 & 125lbs. I have 2 kids. I like my body but i need to get rid of my belly fat. When i gain weight it all goes to my tummy. When i try to work out i lose weight everywhere else but my belly. Please help. im thinking about the Ab lounge or Ab circle

16 years old.
6’0" height
150lb. weight
tall, skinny frame
I need to gain some serious weight in about a month.
Problem: even if i gain weight (in pounds), my arms, chest, and body don’t get thicker in diameter.
Wat is a good routine to build muscle for me fast and gain weight?

I’m not fat at all, but whenever I gain weight, it is in my midsection. School starts on August 21, and I want to look my best. Any tips on flattening my stomach? Any healthy living tips would really be appreciated!!
–Please try to be specific! Like how much I should excercise a day and what kind of cardio.
Thanks!