So I noticed that when I lift my arm my right breast has slight indentation at the bottom - almost making it look flat, but was difficult to see. I've been to the doctor who said she could potentially feel a 'pea-sized' lump so got referred to the breat clinic. The doctor there couldn't feel a lump but I got an ultrasound anyway. They found nothing on the ultrasound after both a student nurse and nurse checked it. However they couldn't offer me any other reason as to why my breast puckering has occurred and just sent me on my way giving me the all clear. It is still very much there (although hasn't change at all) and I'm sure it hasn't always been like that. I'm worried that there is a lump but it's just too early/small to feel or see on the scans. I just can't shake the feeling that something isn't right. 

I'm not sure what to do and I might be overthinking it. Has anyone else been in a similar position? What do people suggest I do?