Hi Pratik,
Our family is not directly affected by Thal-Major, but I thought I could share maybe some general info about lymph glands & swelling. My little girl recently had 2 swollen lymph occipital glands on the back of her head, she has also had the same ones in the side of her neck become quite apparent off and on for the last year and a half. She had her tonsils and adenoids removed about a year ago. While that helped the swelling in her throat it did nothing for the same nodes that keep swelling. I was concerned. Her new pediatrician told us that in children nodes can be very reactive, also that in people who are very thin even as adults they can be very prominent and noticeable. We are still watching hers, if they do not go down or are gone in a couple more weeks they will do further more aggressive testing on them.
I would be persistent in finding an answer to the swelling, being a Thal-Major and receiving transfusions, your doctor may want out rule more serious causes other than allergies, reactions to viruses, etc.
Hope you are well and that they go down soon!