I'm a 76 yr. old female. i had to urine cultures within a week .i had both negative results.i still have frequency with small flow. in no pain,why?

Different reasons: Urinating small amounts frequently can have multiple causes.A bladder irritated by infection is common - if recent antibiotics, culture can be negative. A problem with nervous system (from meds or nerve problem) can be another - if bladder becomes over-distended, small amounts get urinated but bladder remains full. Inflammation w/o infection (eg interstitial cystitis) is another, other causes too