The lump you have described behind the ear seems like a lymph
node which has got infected. The lymph nodes here commonly get infected if you have scalp
or ear infections. If they are not very large and very painful if can be ignored provided you dont have any scalp or ear infection. You could take some painkillers to relive the symptoms and if it continues to be a trouble better to meet a ENT specialist
I hope you found my response to be helpful and informative. If you have any additional concerns I would be happy to address them.