I hav lump under skin on my chest. it isnt like a pimple or anything. its under skin. its hard and sore. what could it b.. could it b like a tumor?

Depends on the size: You can watch this nodule/lump for a few weeks and check if it is growing in size or remaining unchanged. If it is less than one cm in size, you can watch it for changes over the near term. If it is bigger than one cm or if it is growing/increasing in size then you need to consult your doctor and let him/her examine you and give you further advice.