Dear Leijiayang,
The exhaustion and some postpartum depression you are feeling is normal for a young woman who has married and had a baby within a year. That is a lot of changeto go through. A lot of learning was required. First, learning to live together as husband and wife was needed. Then your body worked very hard to build that baby, carry it and deliver it. Now it must care for the little one and be awakened often in the night. Maybe you are nursing? It is said in medicine here that it takes a full two years for a woman to totally recover physically, from a birth.
Give yourself time to recover. You will feel good again, and not tired all the time. Try to eat healthily, and on time, and to get your sleep. Nap when you can. You haven't aged because you have had a baby, you are just very tired. This will pass.
When you feel strong again, look around and find a married woman, older than you are, with a child. Somebody whom you can admire for the way she is stillherself, and her own age, and hasn't turned into a middle-aged lady just becauseshe is married and has had a child. Use her success as an inspiration. This will encourage you that you can feel as good, and be just as young looking and pretty as you were before you had the baby. Your body has changed in some ways, sure, but it will mostly change back again.
Take heart. Don't let those other inexperienced young women make you feel discouraged. Just do the best you can to get your own rest, and to eat healthily. Don't let yourself feel sorry for you, and try not to gain excess weight. The normal weight you gained with pregnancy will fall away again as you take care of the baby, and probably nurse it. If you eat fattening things to comfort yourself, you will find it much harder to get your previous appearance back, and you won't like that. So eat healthily, and try to nap when you can, and get to bed early when possible. This will all pass, and you will be your familiar self again. That is, unless you let yourself believe that you have become middle-aged, and cannot ever have your youth and energy back. Then you may not take care of yourself and your looks, and so you will have changed. It will be up to you.
Just because you see others who look frumpy and have let their looks go, you don't need to do the same. Just wait until you feel good again, and then attend to your appearance. You may not be able to spend the time that you used to, but if you want to look pretty you will manage.
You can become an example for those inexperienced girls who are commiserating with you now, and telling you, in your tiredness, how you "look mature." When their time comes they will need a good example, and you can be it! I was not 21 yet when I was married and had a child ten months later, so I know what I'm talking about. :-)
Warmly, and with my best wishes, Mary.