Are Sagging Breasts With Wrinkled Areola Normal After Childbirth?

Hi doc...
I have developed wrinkles on both my breasts. I am 30 yrs old and have a 4 yr old son. I stopped breast feeding more than 2 yrs back. My breasts sag and my areola and the skin above it wrinkles and retracts especially when i raise both my arms. Pls let me knw if it has got something to do with cancer or is it normal after pregnancy. I lost almost 15 kgs after pregnancy that too within 6 mths. Pls advice