Do a lot of people get de quervain's tenosynovitis?

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.

Pretty common: Pretty common. So it's well known and treated.