Hi I was 24 when i had my first mamogram so i can understand your concerns. The mamogram is not painful at all and is a very simple method , its just like having an xray you dont feel a thing . Im 27 and going in for a second next week , i dont have a mass in breast but its in my arm pit , i also have alot of bone pain , breast pain etc.
Let me know how you get on and i will do the same
Good luck