Sentinel lymph node thrombosis/blood clot?

I had a lumpectomy and sentinel lymph node removal on Nov 19. Everything is healing pretty well except I have this tight cord-like thing in my armpit which is very tight and makes it difficult to lift my arm fully and is somewhat painful. At my follow up appt with my surgeon she said it is a "cord thrombosis" and the cord thing is a vein. My surgeon is Italian and although her English is quite good I feel that she struggled explaining this to me and I'm concerned because it is not getting any better.
Has anyone had any experience with this? I am a fairly active person and this is limiting my mobility, I'm getting discourage because it's not improving at all.
Thanks for any feedback you can provide!
Amy