Recurrent UTI's after Intercourse

[MedQuestionsFromC]

I have experienced recurrent UTI's for the past 2-3 years and have seen a Urologist.  I was on a low dose antibiotic daily that seemed to be effective, but when my husband and I started seeing a fertility specialist I was told to switch to macrobid.  My urologist made this switch but recommended I only take it when I get a UTI.  While I was pregnant I didn't seem to have any issues, but I had a miscarriage 4 weeks ago.  We waited 2 weeks after a D&C procedure to have intercourse and within 2 days I had symptoms of a UTI, so I self-treated (based on past doctor discussions) taking 2 macrobid daily for 3 days.  I then used a test strip over a week later and did not have signs of a UTI so my husband and I had intercourse last night.  I now have symptoms of a UTI (urgency and burning).  We have done everything we can think of to prevent UTI's - urinating before intercourse and right after, showering before and after, increasing water intake before and after, etc...

We are not sure what else to do:
- Could our lubricant be the problem?  We use canola oil because all water based lubricants don't work or cause irritation for me.
- Is it possible that this is part of a larger issue?  When I saw my urologist they used an ultrasound to make sure I can completely empty my bladder, but that is the only diagnostic testing they have done.  What other testing should I ask for?
- it seems like I am extremely uncomfortable before my test strips register an infection.  Is this normal?