Any enhancing area , lesion or swellings in the floor of the mouth can be a salivary gland
swelling , cystic lesion like ranula
, ulcerations or some kind infection arising from adjacent teeth or jaw bone.
As you have mentioned you have undergone surgical resection of the tongue and even radiotherepy for the oral malignancy you had in the past , i would suggest you to get the oral condition examined by the concerned oral surgeon.
Exact diagnosis can be made only after visual examination of the area and pathological tests if recommended.
you may also require an OPG radiograph to confirm the spread and extension of the lesion and the adjacent structures involved which helps in further diagnosis and treatment.
i hope this helps ,