Yes. De Quervain's tenosynovitis very common. It can develop spontaneously or after trauma. I see it commonly in women who recently had children. It develops from a combination of tissue swelling from hormones and from how new mothers lift their babies. Symptoms often resolve spontaneously. Those cases that don't usually respond to a single steroid injection, which is safe while breast feeding.
Yes. This is something that I often see in the office -- a simple corticosteroid shot will often help -- other options include bracing or physical therapy.