Breast-help

I have done self-breast exams for about a year, and in the past 3 months I have felt lumps in my breasts and they're more sensitive than they have been in the past, when I'm not on my period. I talked to my sister about it and she said it was normal but I've heard people say it's not normal. I don't want to make a big deal about it if it's a normal thing. Please help & reply!!