I'm not sure what type of tests you are referring to but I can't imagine that either a Mammogram or Ultrasound (or possibly both) couldn't demonstrate the lump that you feel. Have you had a breast exam by your Physician and the tests that I mentioned. If not I would advise you to do so.
What is your age? Does the lump increase or decrease in size? Is it painful or tender?
Has a mammogram, ultrasound and MRI been done?
Have you noticed any abnormal features on breast self examination like skin changes, breast lump, nipple discharge , etc
Have you seen a breast specialist or your doctor for your symptoms? Till then you could try some warm compresses, breast massage and oral pain relief medications.
Let us know about what your doctor or breast specialist advises.
Let us know if you have any other doubts and also about how you are doing.