Drug Resistance?

So, I have had uti issues my whole life. Since becoming pregnant and now breastfeeding, they have put me on Macrobid, which is not what I usually had. So I have only had it about 5 times in the last year and a half. I have one now and I am on day 4 of my meds. Haven't missed a dose. Been taking it just like instructed but there is no progress. I know I should finish them first, and I plan to. But do you think im just getting to the point where the drug doesnt work anymore? I was on Bactrum for years and my doctor warned me that could happen but so soon? Yes ill be seeing my doctor if it doesn't go away. Maybe it isn't even a uti? idk. just looking for some thoughts.