The sore lump where the antibiotic shot was given is not unusual. These injections are often quite large, which is why they are given in the buttocks. They can leave the area quite sore for a while. I am sorry to hear that your is still hurting you, but it should resolve on its own. The original symptoms of Flu and Tonsillitis could be from several different things. However, the one that comes immediately to mind is mononucleosis. Mononucleosis is a viral infection. It causes very sore throat, often with very enlarge tonsils with a thick white coating on them. It can cause swelling in the neck from enlarged lymph nodes that people often refer to as swollen glands . It can also cause you to have fever, vomiting, diarrhea, and often just feel terrible. Early on the throat and swollen glands can be confused with simple strep throat. Treatment for this (penicillin usually, sometimes as a shot in the butt) might be given. However, unlike simple strep throat which usually gets better quickly the symptoms of mono tend to linger longer, sometimes even for a week or two. They may even come and go over several weeks. You can have a blood test for mononucleosis. Two additional things to note. First, people with mononucleosis should not take amoxicillin. If this is the penicillin you were put on you should ask your doctor about it. It is not dangerous though, and I do not recommend stopping the antibiotic you are on without consulting your physician. The other one is that people with mononucleosis may develop enlargement of their spleen. This can cause a dangerous situation if they were to be injured, such as in contact sports. If this does turn out to be mono this is something you should discuss with your doctor.