I am a seventeen year old male, and I have a small, painless, firm lump on my left leg, near my shin, about the size of a thumb print. I noticed the lump about two days ago, and it hasn't changed very much. It might have gotten a little smaller, or maybe it was just my nerves that made it seem bigger than it was the other day. It doesn't move, and there is no skin discoloration. It's only noticeable when I squat or flex my leg muscles, but otherwise it's hard to feel or see. But when I can feel it, it's a very prominent difference between the shape of the muscle and the mysterious lump. I have never had anything like this before, but some of my family members have had fatty cysts or lumps that appear and disappear on their body. I, however, have never had anything like this appear and it is kind of scaring me. I looked up what it could be, and came up with either a lipoma or soft-tissue sarcoma. I'm making a doctor's appointment tomorrow.
Another weird thing about this, it almost feels like it changes texture with the tension of my legs (softer when my leg is relaxed, harder when flexed) but that wouldn't that mean it was some kind of muscular issue? I have put my legs through a little bit more strain than usual within the past few weeks, and even jumped off a barn roof, but if it was trauma related, I imagine there would be some pain or bruising.
I hope my description is clear enough. Many thanks to all who respond.