Thanks for the query to H.C.M. Forum.
The tumor as you mentioned in your query may be due ,
1 Benign tumor
, previously when doctor first examined 4 years might be a benign tumor, but now this is from 4 years growing its size and become painful , so the condition has worse.
I am sorry to say that the tumor might had changed into malignant form.
and M R I breast will find out the cause and nature of tumor. Can be confirmed by a surgeon as physical examination will find out every thing.
In my opinion your have wasted 4 years and now AT ONCE consult another surgeon and get his opinion and treatment( 3rd one).
Good luck for your mother .