Uti how long

How long does it take to start feeling better I started on Saturday the dose but on Monday the doctor called me because I had left a voicemail saying the pharmacist had found it weird I had gotten that antibiotic back to back so by Monday I started a new one for 2 days but it was making me feel so jittery and heart racing and was advised to stop when I called on Tuesday he said he advised me to go back on the prior one since the test he did said that antibiotic would be the one to help in the urineanaylisis they did