How do i diagnose. I get the results?

I am experiencing a muscle pain on the left side of the neck right up to below the the left ear, similar to stiff neck since last 4 days. I have found a lump near the area (on left side behind the head at the bottom of cranium or skull bone) which I have never noticed before. Now i am also experiencing sore throat. I smoke, but genuinely trying to quit. The current situation has got me extremely panicked. How do I diagnose if I have cancer? And how much will it cost me? And when will I get the results? I have also tried to see in my mouth with torch and hand mirror, the left tonsil seems bigger than the right one. There are no visible white patches but lumpy patches are visible which I usually get when I have sore throat.