Losing weight

Hi I have a peculiar problem. I put on weight but when I put on weight, It's just in my thighs or my butt or lower stomach otherwise no where else I tend to put on weight..I walk almost every day pretty fast and brisk and I don't take too many sweets, I don't put sugar in m milk no ghee but still it's taking me so long to loose weight. What more do you think I can do? I am 23 and I weigh 56 kgs. And is it true that if I join a gym and then leave it after 2 months to continue my walking would I start putting on weight? Because that's what I am hearing and hence I am scared to join a gym.

what si 56 kgs in pounds? because ill give you advicei if you let me knwo and also your heiht is important

I am about 123.4589 pounds and my height is approx 5 feet 3 inches