Recent uncomfortable arm - started anastrazole yesterday

Good morning, just a quick question. Had sentinel node biopsies done 5 weeks ago and have made a good recovery without too much discomfort,  Initially was doing the exercises but am very active and have been able to do everything without problems.

Since yesterday I have had a very tight feeling running down my arm and also strangely quite a stiff thumb! Is this anything at need to be concerned about or is it just normal? As I say I have been perfectly fine until now.

Thanks in advance 

Mary x

p.s. Started Anastrazole yesterday