Large, painful breast lump that is growing fast

I just had a baby on May 27th and I have been breastfeeding. I noticed a small lump in my right breast in the upper left side. It was about the size of a grape around June 18th. Since then it has been increasingly painful and is now about the size of a plum. It is very hard and it no longer moves when I push it. I have tried everything for it if it was a plugged duct but nothing has worked. I went to the doctor and she said it probably wasn't a plugged duct and she has scheduled me for a ultrasound next week but I was hoping to get some ideas on what it is before that. Thank you.

[Cleveland Clinic]

Dear RachL777, Without further evaluation including physical examination it is impossible to say what this is for sure.  Following through with the evaluation as suggested by your doctor is recommended.

[alina gomo]

Hi!
I am 26 years old and one year ago i was having EXACTLY the same problem like you and my lump became like an apple in few months. i was to the dr but in the beggining they said that i am too young to get scared to have breas cancer especially tht i dont hve cases in my family and the send me home asuring me that the lump will disapear. Nothing happend and i went alone and did a biposy and the result was positive: IDC, stage III.Now i am on chemo 6 cycles and then mastectomy and then god knows what! Dont be afraid and dont wait like me too long!Hope 2 hear soon from u, good news.