As it has got much worse and has been causing a lot of pain, I would try and get a sooner appointment.
You clearly do have some form of infection. Could be a boil or an abscess which may require lancing and a course of antibiotics.
Of course, the problem with it being at the back of your thigh is that you are not able to see it properly.
The other symptoms may have no connection with your thigh lump, but still mention them to the doctor. It is very likely that the headache with the blood in the nose is likely to be a sinus infection.
It may be a sits, I would recommend to go get it check out asap.
Maybe it is a boil that is infected. Do you have a fever? It the leg turning black or the lump? Since there is a lot of pain and it is getting bigger I would see the doctor as soon as you can. Also the headaches can be a sign of fever. Do mention the sense of smell being off and blood in the nose and how painful it is. Have you been hiking or gone anywhere outdoors in the last 6 weeks? I'm thinking it can be a Staphyloccus infection. Other possibility a spider bite that got infected with a Staphylococcus bacteria.