when should I get checked for cancer?

Hello everyone! 💕
Okay so I had a pretty serious question. My grandma had breast cancer just a year back. After she beat it my aunt ending up finding out that she had stomach cancer and breast cancer. I was wondering when would I be a good time for me to get checked? I'm 19 years old and cancer is something I've been afraid of my whole life. These past months I've noticed my right breast changing a little bit but I don't know if it's for sure or if I'm just panicked and my mind is playing tricks on me. What do you guys think?