What Causes Abnormal Nipple Discharge?

Hi, I am 40 yr old female with a Mirena device ( IUD). It hasn t expired and gets checked regularly. I recently noticed for first time very tiny sticky discharge on my right nipple only. I freaked out, thought oh no!! I m pregnant!! Then quickly dismissed it due to my friend, physician said, It is almost impossible. Tonight, I noticed it again. It s a very, very, tiny, small amount, sticky, no odor, and looks like milk. I did a self breast exam and no nodules, lumps, bumps, nipples aren t sore, normal color. I have also been gaining weight like crazy! Could I really be pregnant? If, not what the heck is happening to me? Sincerely, Freaked out!!