I'm starting to feel weird like I was walking down a case of stairs and I hit my breasts and it hurt a lot idk if I'm starting my period yet I found something sticky in my underwear tho

Puffy or sore boobs and sticky discharge are totally normal signs that your body is getting ready for your period, so that sounds exactly right.

Okay so your breasts will probably be sore sometimes as they grow, and that totally makes sense because they are growing really fast! They get super sensitive because hormones are literally making changes in that area. It's not just when you hit them; sometimes they can just be tender for no reason, or feel heavy. That sticky stuff is probably vaginal discharge, and it's also a sign that things are moving along. It's your body's way of cleaning itself and getting ready for your first period.

Every body is different, but for lots of us, this is exactly what happens in the months or even a year or two before your first period actually starts. Your boobs get sore, and you start noticing discharge, and eventually your period will show up. There's nothing you have to do right now except know that it's all part of growing up, and it's totally normal. Some people wear a soft bra or a sports bra if their breasts are feeling extra sensitive, just for a little comfort.

If you want to find out roughly when yours might be coming, there's a quiz on this site: how close is my first period? — it's super quick.