13 years ago I too had a mastecomy, removal of eleven lymph glands.
I had chemo and radiotherapy,
I took Tamoxifen first and then when it came available Arimidex.
You have been well for 4 years now, which is quite a long time since your treatment, so there is good reason for you to be very positive.
I have two friends who have also been in this position.
One had it ll yrs ago, and the other 15ys.
There are a lot of us survivers out there, so dont worry about it for too long.
Ive been away for the bank holiday, so Ive only just seen your post. Best wishes.