SNS lowered milk supply

I had my baby nov 23 and have struggled with bf since I started. One week pp and she lost a pound so her pediatrician said we needed to supplement. I started using the lact-aid supplemental nursing system and have noticed a large drop in milk supply. I'm so frustrated. The latch is still a struggle, my nipples are raw and now my supply is low. Also when I have my milk come in it is painful. Is that normal? Anyone else go through these struggles and still manage to get things back on track?