I'm worried about my health

It actually sounds like you're underweight. I think thought if you've been to the doctor since you got your period, and he/she said nothing about your weight, you're probably ok. If you do want to gain some muscle, you could start lifting light weights.

This is typical of a fourteen year old female who is starting puberty. Iam assuming that you are pretty active, and that you have a pretty high mtabolic rate. You will start sleeping more now that you are begining your teenage years; because your body shall be going through more changes which will require more rest and recooperation time. Eventually you will fill out and gain the weight that is desired. dont worry you are a perfectly normal teenager. Try going to the gym and doing some strength training as this will benifit you. It will help shape your body; further more it is proven that people who stength train during their adolescent years shall keep the shape (in women especially the curves) of the body that they build for the rest of their lives.