What Causes Lump In Breast Along With Pain?

I'm a 24 year old female & I have alump in my breast, It's not swollen my breast it's slightly painful and makes it extremly uncomfortable to wear a bra I've been to my GP today and he hasn't given me any suggestions to what it could be but he said it won't be cancer due to my age (which i disagreed with as i know anyone any age can get cancer) I suggested mastitis as I have the symptoms more closer to that than cancer? (& i know i shouldn't self diagnos but just wanted to have a outline of possibilities) i'm been referred to breast clinic for tests but will take 2-3 weeks for the referal is there any chance it could be something else as my GP wasn't helpful and hasn't given me anything for the discomfort please hope you can help as I have a 5year old child and i'm a single parent and this is very scary please