Pain behind my ear. I try to feel of there are any lumps but don't feel anything. Is it possible to get a swollen lymph node without any lumps?

No. Swollen lymph nodes indicate the presence of a lump. If there is pain behind ear consider the mastoid as the site from which the pain arises. This area should be checked by an ENT doctor. The other structure just behind the ear can be tail of parotid and this structure should also be checked if pain persists.