I do not think that this is some sort of cancer but you need to have it excised under local anesthetic and a section microscopically examined.
It could be a benign lipoma, triggered by the original trauma (bug bite),
however, please do not "sit" on it for another ...5 years, specially now that it has grown larger and irregularly shaped. Have it checked for your own peace of mind and removed for aesthetic reasons, if benign.
I had one on my upper back, which the doctor removed in less than 5 minutes! That was many years ago. I had almost forgotten about it!
Best wishes,
Niko