Hi Irina,
I am so sorry that you have breast cancer. The fact that the surgeon did not get into the muscle is a good thing, though. It means he saw no cancer there and it will also mean a quicker recovery for you.
I certainly couldn't lift my arm over my head for weeks after my surgery (I had a mastectomy and lymph nodes removed). The second week was actually worse than the first and then things started to improve. Ask your doctor or oncology nurse to give you some exercises that you can do to help restore mobility.
It is always a good idea to keep the lines of communication open with your surgeon. He may want to prescribe something for pain and he will certainly want to make sure that you don't have an infection.
Good luck and stay in touch.
Laurie