Hello,
Welcome to the ehealthforum and I am really glad to help you out.
Most lumps behind the ear are due to infections or benign tumors of soft tissue origin. Behind the ear there is skin, fat, cartilage, bone, nerves, blood vessels, Lymph nodes, and salivary gland tissue (a portion of the parotid salivary gland extends behind the ear). A bump can develop from any of those structures, and could be due to a tumor (benign or not), an infection (Lymph node or skin), a swollen muscle or salivary gland, etc.
If the lumps are there in the neck also then swollen lymph nodes should be ruled out.
My suggestion would be to wait it out for a few weeks to see if it changes in size. If it gets smaller, it was nothing. If it happens to get bigger, then make an appointment with your doctor.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care.