I wouldn't be overly alarmed. More often than not these things turn out to be nothing to worry about. As you know, with Boxers any lumps, bumps or growths do need to be watched. Sounds like your vet is on the ball in finding the first one. I would just be guided by the advice of your vet and try not to worry too much.
Sending positive thoughts and best wishes to you and your baby.
Sending positive thoughts and best wishes to you and your baby.