How does a lump feel like?

Hello, i am 21 years old. Today i felt a lump about the size of marble on my right breast and then when i grabbed it and held it properly it felt much bigger - about the size of a tennis ball - . If i try and squeeze or push it, i can move the lump along to the left or right, or up or down. Its literally feels like theres a tennis ball inside my breast that i can push around a bit. It doesn't hurt yet. My nipples have been very wrinkly for months. No discharge that ive noticed. The lump can't be seen from the surface but can be felt when you touch the area, and then can be held and moved when u squeeze it. Its very hard and big. My mothers mother and fathers father both passed away from cancer so i am very stressed. Any advice? I will try book a doctors appointment but am making this post to calm my nerves. Thanks!