How do i know if any lump is cancerous - #9815

I have a pea size,a little jelly texture, moves put i put my finger on it , its near my posterior cervical , i first found it on March 21st and i am not sure when I should get it checked and what could be the reason ...its not painful but I pressed it to much and my nail has made scratches on it only that hurts and i occasionally have ear pain in both my ears ...comes goes i don't know and I have a history of sinus