your are a feeding mother, the reasons for pain may be two factors one is because of muscle spasm due to abnormal position while feeding baby or second possibility is when breasts are filled with milk in large quantity they swell , become hard and pain and tenderness follows till you feed your baby.once fed pain relieves.
if its due to muscle spasm it relieves by peripherally acting muscle relaxants such as keflex
as you mentioned.
you need to sit upright and support your back against wall and keep a pillow on your lap and place your baby and feed. this is all sufficient as there is nothing to worry.