It is certainly possible for tonsil tissues to grow back especially if it was not removed completely (depending on whether a tonsillectomy - complete removal of the tonsil or tonsillotomy - partial or near complete removal of the tonsil was performed). Regrowths of tonsillar tissues after tonsillectomy is however rare.
It may be possible that the "regrowths" are benign lumps from tonsillar tissues such as cysts, fibroma, papillomas or lipomas. I would suggest that you have the lump assessed by an ENT Specialist.
Hope this helps and all the best!
