Should I Be Worried About A Lump In My Armpit?

Question : I am a 39 yo female and discovered a tiny lump in my armpit almost three weeks ago. I immediately went to my doctor, who said he doesn't think it's anything to worry about, but he's sending me for a digital diagnostic mammogram. I'm not sure if he's just trying to keep me calm, and I want to know how concerned I should be about this because I've been very anxious and miserable. The lump is about 1 or 2 millimeters, and seems to be attached to my skin because, when I relax my arm, I can move it around, though it always seems to be in the same spot on my skin. It does appear to be under my skin though, and not a pimple or infected follicle, etc. It feels roundish or ovalish. I don't use a razor or deoderant, so that is no the cause. I just want to say that I am going for the diagnostic mammogram on Tuesday, and what I'm looking for is a professional opinion of what this is most likely to be based on my symptoms. I just feel so anxious because I know there is something there, and I don't know what it is, and I can't get any consistent answers from reading online. I know a diagnosis can't be done online, but I'd like to know how likely this is to be serious. Sorry, one more note: I'm pretty health conscious so I get blood work every year and it always comes back normal. I had my most recent physical/blood work in September and all was good. I'm 5'4", 115 lbs, and vegetarian (except occasional fish).

I'm sorry, I don't understand this answer. My question was - what are the odds that this is something serious, based on my symptoms?

Thank you. So, just to clarify, you think a 2 millimeter lump under my armpit is very unlikely to be cancer?

What do you think it is?

Thank you. I had my diagnostic mammogram (and ultrasound) today and it was a sebaceous cyst. I appreciate your help.