that's a fair size lump it sounds a bit bigger than a pea maybe a chick pea. I would be hoping it might be forming scar tissue or perhaps granulation tissue which sometimes forms from having a fair sized wound. It doesn't often grow. Surprisingly, benign tumors do grow - so it could be something benign.

Bottom line... You want it out. No matter what it is it has no business being there.

Once you get the results then you'll be able to breath easier regardless of the results because at least then you can have some type of answer.

best of luck