UTI and unknown Pregnancy

Hello. I just want to get opinions from someone because I am really confused and nervous. To start, as of February 19th I had a very short and very light (for me) menstrual cycle. And it was an odd brownish color. I took a pregnancy test the day before since I hadn't started yet and was supposed to and it was negative. Then in the following weeks I have had some odd symptoms such a increased breast tenderness, muscle ache, headaches, fatigue, and nausea that comes and goes (mostly at night). During this time I took 4 more pregnancy tests that all were negative. I called my doctor and explained how I was feeling and he told me to come in. I took a urine pregnancy test there and it was negative, however, the nurse said she thought I had a UTI. My doctor kind of blew that suggestion off but did want me to come back for another urine test and a blood test which is scheduled for 10 days from today (March 14) and also switched my birth control to BEYAZ which I believe has folic acid in it in case of pregnancy. I haven't had symptoms of a UTI but then again I have never had one so I am not quite sure how that would feel anyway. Also, I do not think that I am pregnant and am not trying to conceive. My concern is this: Can letting a UTI go untreated for about a month (when I could get back in to my doctor for an appt.) cause a possible miscarriage or any harm to the baby if I do end up being pregnant? It is seriously scaring me. Though I am not trying to have a child I would never ever want to do anything to endanger the baby if it happened. I want to know that the baby isn't in any potential danger if my doctor is incorrect and I do have a UTI and am indeed pregnant. Any help, suggestions, or comments will be very, very greatly appreciated.
Thank you!