I need some advice! Please answer!!!! lumps....?

am a 15 year old girl, And I have a lump on the side of my neck. I have one on my right side of my neck thats about 1 centimeter in length and its movable and its kinda hard. I also have one on my left side and its very tiny, about pea size, and its also movable and sorta hard. Should I be worried about these? I have been to the doctor many times and they have felt the lumps there many times, and never said it was anything. My brother also has these same type of lumps on his neck, so is it hereditary? He got his checked and it was just fatty tissue, or lymph nodes...i dont remember. But anyways, I just dont think its anything since my dr's know they are there, and I have no other symptoms that it can be anything serious! The lumps have been there for at least 6 years, or longer! I can remember them there for a LONG time! My parents know about these and have mentioned them to the doctor and they said it was nothing... They do not hurt at all and have not grown in size since they have been there!