Felt by all but not seen. ILC concern?

I don't know how to be short and sweet, lol.

I'm 27. Earlier today I had my mammogram as well as an ultrasound. The techs and doctor all felt the area of palpable concern, though nothing at all showed on any of the imaging. While I am obviously glad that nothing of obvious concern was visible on US and Mammo, I still have this hard area on my breast with no definitive answer given as to what this is. I was given possibilities like could be this or could be that but I am not comfortable with just accepting that nothing is wrong without knowing what the hard mass on my breast actually is. Would you be?

While I am comforted by the fact that a number of things are in my favor, it is not enough. I have a hard, palpable mass at 12 o'clock on my right breast. It's not what I would call a lump and it is like nothing felt anywhere else on either breast. It is thick, hard and immobile but definitely more spread out and flat with some crags than any kind of distinct lump you would call a marble or pebble or things like that most people talk about. It's maybe an inch and half or so. It's hard to tell for sure because part of it I can feel a definite edge but then other sides seem to go into the surrounding tissue. It doesn't hurt touching it all. I found it 3 weeks ago during a self-breast exam. After the first couple days, I have basically left it alone, other than brushing my hand lightly over it every few days, hoping maybe it magically disappeared. However, now, I can spot the area even upon visual inspection alone and absolutely feel it without even trying. About a week after finding it I began getting occasional piercing pain on this breast but more on the upper inside…stop what I'm doing and clutch my breast in excruciating pain kind of pain. In the past week or so I just feel a kind of pulling, pressure and heaviness coming from the area in question and perhaps a bit of a stinging/tingling as well.

TBH, my greatest concern would be ILC. Though I know stats and facts on ILC are in my favor, I have read enough on here and elsewhere (damn you Dr. Google, I know) to know that ILC is typically hard and flat like mine and often doesn't show on mammograms and ultrasound, also like mine. I have also known someone diagnosed in their 20's as well. I certainly hope this is not the case but I would hate to rule it out being as sneaky as it is.

I want a biopsy. Core needle biopsy I would think. Am I crazy? Do you think there is any chance of insurance covering this when imaging shows nothing? Is there a benign condition that this CLEARLY sounds like that wouldn't show up on any imaging? I was recently approved for Medicaid through United Healthcare Compass Plus after finding out I don't have enough work credits to qualify for disability despite some disabling health conditions (ehlers danlos syndrome, hemiplegic migraines).What would your recommendations be? I think I am remaining fairly calm considering, but still, I feel like I need to advocate for myself and like I need a definitive answer about this hard mass.