Baby biting while breastfeeding!

Melissa
My almost 5-month old (no teeth yet, thank goodness!) has started biting down while feeding, and pulls my nipple like playdoh, then smiles and looks at me like she is so proud!  At the same time she continuously hits me in the chest or face with her fist.  Any tips to make breasfeeding more enjoyable?  Or have we just reached a tough age??