Hi Mihoko,
Welcome to the site. That seems like a pretty great age to start HRT. I wanted to let you know there is a category here called Youth Talk; where you can share experiences with others as well. You are welcome almost anywhere on the site, it is just for younger folks there.
Bear in mind that everyone's weight, metabolism and chemical make up (not to mention age) makes each journey unique. So, while I can talk to my experience and those of others, yours will not be exactly the same.
I would suggest that at 15 you should not try to gain weight unless your primary doctor thinks you are under weight. As one gets older, fat kind of just collects. It becomes harder to keep off and (not sure if this is an myth- a miss myth if you will) it is harder for women to get fat off and keep it off.
The first things I noticed were a relaxation of the mind and smoothing of the skin. I still sometimes run my hand over the other amazed at how smooth it is. Your skin will become thinner with smaller pores. That's pretty cool too but allows you to bruise and cut your skin more easily. I finally realized I could experience emotions in a way I never could before. I started experiencing tingling, sensitivity and pain by my nipples about a month in.
I have heard(and experienced a little) about the eye thing. I don't know how drastic a change it has been for others. For me I had hazel eyes that depending on my mood shifted between brown and green. Now, about a year later, they are more green most of the time.
I also want to share some links with you. They are mostly welcome information and the rules that govern the site. If you have not had a chance to look through them, please take a moment:
Things that you should read
Once again, welcome to Susan's. Look around, ask questions and join in.
With warmth,
Joanna
PS: I am going to move this into a section under transitioning(I think) then the category is HRT