Dear bac432: It is difficult to tell whether or not you should be concerned. It seems that, at a minimum, your mammograms are hard to read due to dense breast tissue. Usually a spot compression is done to further define an area of concern. If there is a suspicious nodule, it may make sense to see a breast specialist to determine if this needs further evaluation.
Plan B would be to have a biopsy of the area (I'm assuming the xrays were all of the same area.) For an area that shows on mammogram but can't be felt, it's done with an xray guided procedure called stereotactic biopsy. If the area remains of concern after all the studies you describe, it sounds like it might be a good idea.