OP, hopefully you're on your way to hospital by now, hopefully in an ambulance with switched on paramedics who can see what is going on and that it's not an 'antibiotics and rest at home for a few days' job but a nasty infection that's well on the way to being cellulitis or sepsis and treat you accordingly as well as have the hospital on standby to treat you as soon as you get there.
Given that there are plenty of people on here who think that it looks like it could be the early stages of sepsis and you have already had sepsis previously, I think that you would be justified in saying to them 'I think I have sepsis. I have lupus and am immunosuppressed, I have had sepsis before, I take methotrexate, I am prone to DVTs and take anti coagulants but was given xxx antibiotics earlier today which I have just read I shouldn't mix with the anticoagulants. Despite taking the antibiotics, my symptoms are getting worse. If this is sepsis and you don't treat it, what will happen - in an hour, in 12 hours, in 24 hours? If this isn't sepsis but something different and you treat it as if it were sepsis, what will happen - in an hour, in 12 hours, in 24 hours? What is the hospital protocol when sepsis is suspected? Why do you think I don't have sepsis given that I have the following symptoms that can be sepsis [then list them]?
If you are sitting at a and e waiting, maybe it would be worth writing a list similar to this out (or copying this on your phone and tweaking it to make it fit your symptoms) - hopefully some of the other people on here who are medics can tell you exactly what to say given what they recognise from this thread, so that you have a paragraph or list of symptoms / issues on a piece of paper or on your phone to thrust at the doctor or nurse or triage nurse to get somebody's attention if they are ignoring you.
There was a horrible case at my local hospital a while ago where a patient had gone to her GP, been diagnosed with meningitis and sent down to the hospital with a covering letter that basically said - this patient has menigitis, please treat urgently. Unfortunately she was a regular at a and e as she also had cystic fibrosis. When she got there, they assumed that she was there because of her CF - put her in a bed, said they were busy, didn't even look at the letter and said that she wasn't usually urgent, they were busy and would be back soon... It wasn't soon enough sadly and she died - basically because they jumped to assumptions because they knew her, were busy and wouldn't stop to listen to her say that it wasn't her CF that was the issue. If you go to the hospital now, every desk and booth in a and e seems to have posters and protocols and info about what to do if it is even suspected sepsis (for adults - pretty much treat immediately as if it is, the risk of not treating it is much more dangerous to the patient than of being wrongly treated).
Or maybe just go for the blunt 'if this is sepsis and you don't treat it, what are my chances of still being alive tomorrow morning? What about the morning after that?'
Good luck OP - sorry this is a bit long, but hopefully you are being treated and won't need it! And if you do, that it will make sense...