Concerned I have IBC

Hello. I am a 22 year old female and have never been pregnant/breast fed. Around three months ago my right nipple became inverted. I really didn't think anything of it at the time, I thought it was fairly common and just a problem aesthetically, plus at the time i was having other health problems (terrible migraines that were eventually just put down to work related stress by my doctor after lots of blood tests and brain scan), so I basically ignored the nipple and wasn't worried about it.

Three weeks ago while on holiday I felt a lump in my right breast. It was already fairly big, probably about the size of a large.. grape, maybe bigger. I'm really not sure if it had just shown up suddenly or had been there a while, I have very large breasts that are naturally quite lumpy and to be honest (and now I feel really stupid about it) I very rarely check them and I don't actually know how to properly check them, plus I feel that a new small lump may be hard to notice in my breasts due to the size of them. But this was a definite lump that wasn't always there, and then combined with my recently inverted nipple I began to worry a bit.

 I got home from holiday last week and got the first doctors appointment I could which was last friday (5th aug). The doctor didn't seem worried. She said due to my young age it was very very unlikely to be anything (and wasn't concerned at all about the inverted nipple?), but she felt a lump and would therefore send me for a mammogram/ultrasound in 2-3 weeks but it was probably an infection as I'm young. At the time of the doctors appointment I wasn't in pain, but since then the lump seems to have grown, I have been experiencing a lot of pain. My breast is hot to touch (I don't have a fever), it feels very hard all over and extremely heavy. My nipple has been hurting too, a burning sensation that comes and goes and above my nipple there is what looks like bruising developing and the vein that runs down my breast appears a lot more prominent. On friday I had virtually no pain, besides feeling a LITTLE uncomfortable when examined, but since then this has all developed very suddenly and I am in A LOT of pain, like, I can barely remove my breast from my bra because it hurts to touch it, and when I take off my bra and my breast isn't supported it really really hurts. There is a constant ache with occassional stabbing pains even when i'm not touching it, just sitting here now.

 So obviously I know something is wrong now. Perhaps I have an infection, I've read about mastitis but I have never breast fed and I don't have a fever or a raised temperature whatsoever. I also found out since friday that my dad's mother had breast cancer when she was 25 and eventually died of it when she was about 30. My doctor on friday wasn't aware of this, I said I knew my grandmother had cancer but I didn't know it was breast cancer (she died when my dad was less than a year old, so we never really talked about her) and I wasn't aware she developed it so young. 

 I am still waiting for my mammogram appointment to be sent through the post. Yesterday I thought about going to A&E because I was in a lot of pain and worrying that 1) if it is an infection then it might spread too quickly before I get my appointment and 2) if it is cancer then.. well i don't know. I ended up not going and today I feel like I'm in more pain. I rung the doctors surgery and I have an emergency appointment in a few hours. They told me not to go to A&E. I'm not sure what I'm asking you all, just I'm worried that the doctor is just going to tell me it is an infection without obviously being certain, because I am "young" and because I have a lump when it is apparently uncommon to have a lump with IBC. Obviously from researching on the internet I realise that young people do get IBC, and some people do get lumps with it too.

I guess I want to know whether IBC symptoms can develop that quickly (from having no pain to 5 days later having lots of pain, growth of the lump and heaviness/hardness, bruising) and what you think I should do. 

Thank you all for reading this, I realise it's very very long!