Why you smell different now
During puberty, new sweat glands become active in the armpits and private areas.
Sweat itself has almost no smell. Body odour happens when bacteria on the skin break down sweat.
Feet can also get smelly because they sweat a lot inside shoes.
Simple habits
Bathe every day with soap, especially in hot weather and after sport. Pay attention to armpits, groin and feet.
Wear clean underwear, socks and vests every day. Cotton clothes let skin breathe.
Dry yourself well, including between your toes. Let shoes air out, and alternate pairs if you can.
Deodorants and antiperspirants
A deodorant covers smell. An antiperspirant reduces sweating. Both are optional, and both are safe for most young people.
Use them on clean, dry skin. If one makes your skin itchy or red, stop using it.
Perfume does not replace washing. It just mixes with the smell.
When sweat is a problem
Some people sweat a lot even when they are cool and calm, so much that it soaks clothes or drips from hands. This is called hyperhidrosis, and a doctor can help.
Sudden night sweats, or a strong smell that does not go away with washing, are also worth asking a doctor about.