Several years ago I noticed a small lump on the side of my trachea which was soft to the touch but not painful at all. Over several days it became larger and began to interfere when swallowing, that is kind of clicking when the lump rolled over the normal trachea movement. I was living in Japan at the time and after an ultrasound, the doctor said that while 99% sure not a cancer, it was some kind of sac filled with fluid that could only be operated out unless it went away by itself. I dont recall well his analysis but something along those lines if I remember correctly.
Well, it started to get smaller and then went away completely.

Until now about three years later! I woke up one morning with discomfort in the same area thinking I had slept in a bad neck position. The area started to swell over a few days and started to become the same shape and location as the lump several years before.
While not having gone to the Doctor as yet, the lump has not only increased larger than last time, but it is also painful when swallowing and painful to touch. The area is quite swollen more than the first time.

I am wondering if anyone knows what this may be and what the first Doctor meant by some sac on the trachea from childhood - or something to that effect? Perhaps it is infected causing greater swelling/discomfort this time? There are no other symptoms at all except for the swelling on the neck.

Grateful any advice if someone may be familiar with this! Thanks.