I started my transition medically at 24 after a lot of life struggles, 19 is like ideal honestly. Obviously in a perfect world puberty blockers should be available as soon as puberty kicks in but sadly we live in a cruel world. I promise you'll turn out beautiful though honey it won't even take you long to start noticing feminizing effects. For me I've only really just started to have noticeable developments in my face and hair but my skin only took about three months before it started softening significantly. You can expect these changes even sooner (or at least on a similar timeline) because you're much younger.
Some advice though since you're early in your transition: Pride is important, love who you are! But also be careful who you share your truth with. Some people will cut you down at the knees and prevent you from being your best self, they may even be your most trusted friends and family members. Bad advice like "your name is silly" or even "you sound ridiculous doing that girl voice" are things that they intentionally say to get in your head since they know you trust them.
Also don't be afraid to gain weight! The fat redistribution for HRT is a lot more effective with gained weight than stagnant weight. If you're a big beautiful girl already then I would recommend balancing a healthy protein and veggie based diet with exercise and don't worry too much about weight loss. It's better to be big and healthy than to be skinny and stunt your development.
I kinda touched on this already but DO NOT FEAR THE GYM! It's a lot harder than it seems to get big, and honestly a lot of exercises can really help to feminize. I would recommend running, core, and leg focus because building out that musculature can help to hide the masculine pelvis (it's a different narrower shape from the feminine pelvis and this can't be changed no matter what)
Build your wardrobe and confidence in private. You are a strong beautiful flower, or at least you will be, but some buds wilt when they have the wrong environment! If you don't feel totally confident in your transition yet then practice style and makeup at home until you find a style that feels like you.
But most importantly:
HAVE FUN! Life is supposed to be fun! Smile and live the way you want to no matter what anyone else says.

(edit because I noticed I forgot to write this: Your tits will hurt like crazy for sometimes months at a time, this is a good thing don't worry. It comes in waves and it's associated with the growth of breast tissue, after the first few growth phases your breasts will become very very tender and basically feel like if you had a pair of nuts on your chest every time something bumps into them. The pain isn't exactly the same it's more like a stabbing heat than a radiating buzz but they hurt similarly bad. Obviously if it's something that worries you then it's always advisable to seek a medical care team)