I have a painful hard lump that appeared inside of my tongue, it's probably nickel sized. what could this be?

Do you recall any trauma to your tongue? Was there a blister like area before the lump appeared? If so it could be a herpes lesion. A growth is a less likely possibility. I recommend consulting an oral surgeon or ENT specialist for evaluation & advice.

Please see an oral surgeon for an evaluation. It may be a result of trauma, but without a full medical history and an examination it is hard to tell what it might be.