Sounds like a nipple Vasospam.  Maybe Raynaud's Phenomenon.  Avoiding
cold stress is a good idea.  BF in warm environment and wear warm
clothing.  No smoking because it is shown to increase vascular
resistance by 100% and decrease cutaneous blood flow by 40%.  Caffeine
can be a problem too. Moderate exercise has been shown to help.  The
use of calcium and magnesium supplementation has been shown to help,
but hasn't been proved scientifically.  Evening Primrose oil too.
Laureen Lawlor-Smith has done a lot of work on this, you may want to
find her.

Heidi C. Lunn, M.S., I.B.C.L.C.
Miami, FL