STC... this is very common. I am sure that they did a neck dissection and this is what is causing the lymphedema. It's very very normal. You mention removal of cancer from the tongue. I am assuming that the treatment you received was removal of the tumor (possible reconstruction if it was a large enough chunk) then a neck dissection? If so are you going for radiation and chemo? Radiation believe it or not helps with the swelling (it shrinks tissue).

If you are clear (had a clear scan) - aren't undergoing more treatment... then you can go for lymphatic massage. They removed the plumbing in your neck - this causes pooling of fluid. Lymphatic massage helps build new drainage pathways and move fluid along. You can eventually do it at home if you want to. This happens with the tongue for a while as well. It's all collected. I found certain foods irritated it and caused it, how I slept, the temperature of foods. This went on for a long time, but it gets better over time.

best of luck.