I am 23 yrs old girl and my height is 5.1/2 I am actually thin girl 44kg but my breasts alone are heavy,what can I do to reduce them!

Surgery.

Sorry, but you can't reduce breast size without losing weight unless you go under the knife.

However, a really good miniminising bra can go a long way to making you look more petite and to supporting your breasts so they don't get in your way.