Can One Tablet Of Alprim Already Feel Like It Is

can one tablet of alprim already feel like it is working,I went to the doctor yesterday,I was worried about having the feeling of going to the toilet a lot,but no pain,he did not see any infection in the urin,but a bit of blood,but he did think it is an infection,so he gav me alprim to take for 7 days,it was feeling a bit better this morning.and have not so often had to go to the toilet today.
I am 71. Regards Lena