indentations on both breasts

3 years ago I noticed an indentation on my breast. I have indentations on both breasts under my nipples on the bottom of breast when I raise my arm. They are in the same area but the right side it is more noticeable. My right breast has always been slightly larger than my left. I went to my OBgyn and he examined the area and told me that he didn't feel anything suspicious and did not do any tests because I was only 25 at the time. I had another baby and haven't thought much about it. Last week I started having pain if I moved my arm a certain way. This made me start to worry about breast cancer again and thinking maybe he should have done an ultrasound or something. The pain I had has since subsided. If i've had it for 3 years do you think its anything to worry about. I have had 4 children and I am obese. My weight has fluctuated up and down over the past 10 years. I am going to go see another doctor soon for a yearly examination but am very nervous thinking about if it is cancer then it has been there for years.