I have a mildly painful lump on lip for about 2 and a half weeks could it be because i don't clean my teeth enough ?

Probably not: But I would have it checked out by a dentist or oral surgeon because any lesion that does not resolve on its own within 2 weeks should be evaluated.

I doubt it: But any lesion of greater than 2 week's duration must be evaluated. Please see a specialist Oral Pathologist or a specialist Oral Surgeon. Please also see a General Dentist for a full int-oral examination nation, professional cleaning, and most of all an instruction session I appropriate oral hygiene. Failure to do so WILL result in your requiring false teeth at a very early age.