I am 19 year old. i feel a lump in upper lateral portion of left breast. its painless and little motile. is it surely a fibro adenoma?

It could be, but...: ...It's best to be seen by a breast surgeon, just to be sure. At that time we can do an ultrasound +/- a (nonsurgical) biopsy, confirm the diagnosis and decide the best course of rx (which is often just observation). I suggest you ask your gyne for a referral.

Not sure: This requires an exam to assess what it is. See your doctor!