I have a non painful lump underneath my tongue which seems to have a yellow "head" on it. any ideas what it could be and should i be worried?

Possible stone: In salivary duct, but these things are usually somewhat painful. It doesn't sound like a cancerous growth, but always possible. If it persists, show it to a doctor. Painless lumps are always worrisome for cancer.

Can't tell: Could be many things. Probably benign, but always the chance it's not. Please see your dentist or an oral surgeon for examination and evaluation. You know the old adage of better safe than sorry.

Yellow firm lump: Under the tongue needs evaluation. I have removed several similarly described lesions over the years that were benign. Usually lipoma's (a fatty tumor), but one is never sure until evaluation and biopsy. Please get this checked out with an oral surgeon in your area.