Lump on not a cyst?

Friday I discovered a lump on my right , since then it came very sore. I made a doctors appointment today and had a sonogram done. It revealed NOTHING. No cyst. No lump. The doctor said it was just normal tissue. So did another doctor that was there. He said it would likely go down when my period (which is due in a few days) was over. Has anyone else ever experienced this? The pain is horrible when wearing a bra or anytime my presses against something. Any advice?