10 points for best answer! Please answer. Im 15 and scared!?

I am a healthy 15 year old girl. I have had a lump on the right side of my neck for as long as I can remember and it is about dime size and hard and is movable. I also have a pea size lump on the left side of my neck that is hard and movable. I noticed a lump on the back of my neck that is hard and movable tonight. Should I be worried about these? I have gone to the doctor and they must feel them when they check my lymph nodes cuz I can feel them feel them and they have never said anything about them. My brother has the same lumps on his neck and has had them checked and tested and they are just fatty tissue. Is that what mine Are? I'm going to the doctor soon for my arm. And my mom said she is going to metion it to the doctor. I'm scared of what the doctor is going to say! Any ideaS on what it could be? And if you think they are swollen lymph nodes then why would they be constantwly swollen? I had bronchitis when I was 6 weeks old' pneumonia 3 times by the time I was 3, ear infections about every other month for a while and 3 febral seizures when I was young. I now have mild asthma and mild scoliosis. Just in case those things help at all on what the lumps could be. I don't have any medical issues like I used to and am healthy now. The lumps do not hurt at all.