If your using the bathroom very frequently do you say Asher Yatzer after each time?
If he forgot to recite the first time, he recites it only once later.
However, if one is taking a medication causing him to urinate frequently, is different, as he has intention of clearing his intestinal tract completely and does not divert his attention from this process until it is complete. Until that time, therefore, he should not recite the blessing Asher Yatzar.
Likewise, if one left the bathroom but has not diverted their attention to other matters, as he is still wishes to try again, he should not recite Asher Yatzar yet, until he finishes.
עפ”י שוע”ר סי’ ז סעי’ ג, וסעי׳ ו. א״א מבוטשאטש. שו״ת קול אליהו ב, א. וכל׳ השו״ע שם ג: והסיח דעתו. וכן אדה״ז שם ג.