throat ulcer for 9 weeks

i have had a throat ulcer for 9 weeks now. the pain comes and goes, but when the pain is there it is extremely painful and it is hard to swallow and talk. the pain comes when I eat/talk most of the time. the soreness is only on the right side of my throat. i have had a swab done and a blood test for glandular fever and other things but all results came back normal. i also took a course of penicillin antibiotics but it didn’t help/work. the ulcer is circular and white, and the pain is in the back of my throat and also further down my throat. i am so terrified this is mouth cancer. i have so many of the symptoms and have been told they will go by discos so much. please could you let me know if you suspect it is cancer and how i can get it checked earlier than my appointment on the 26th of april if possible. i am so scared and only 16. please help me.