I have had a mirena (levonorgestrel) IUD for a year now. Just recently I have been experiencing cramps, a little bleeding and breast tenderness. Is this normal?

Most likely normal. Mirena (levonorgestrel) wont stop your ovaries from going through its normal production of estrogen and Progesterone even though there is no period. Sometimes the normal hormonal changes can give you the symptoms. As well it is common to have occasional bleeding through the mirena (levonorgestrel).