I was wondering if I could have messed this up. I got the first Hep B shot on Thursday and took an antibiotic the next day as I was feeling an urinary tract infection coming on as well as a yeast. Did I mess my body up more by doing this? I had antibiotics from about a month ago that I didn't use after the doctor prescribed them to me because it turned out I wasn't sick. Ugh! I'm afraid my body is really messed up right now.

You're fine -- at least insofar as the Hepatitis B shot is concerned. The antibiotic won't interfere with the action of the Hepatitis B vaccine.

Be careful about antibiotics. If you fail to use the complete course of antibiotics you could be subjecting yourself to developing resistant strains of bacteria within your body (to say nothing of resistant strains developing in the entire population). Resistant strains of bacteria can really mess up your body.

No the antibiotic will not interfere with the Hep B shot. What does sound worrisome is that you are trying to self dx and treat yourself for a UTI. When a doctor treats you for a UTI they will culture your urine. They may start you on one antibiotic but then switch you within a couple of days once they find out which antibiotic is the one that is most effective to rid you of the bacteria in your urine. It may be the one they started you on or you may be a different one. One more thing that caught my attention is you said, " I was feeling an urinary tract infection coming on as well as a yeast" If you were feeling the symptoms of a yeast infection the last thing you would want to take is any antibiotic as this would make that worse. Antibiotics "sweeten" the environment for yeast to over multiply out of control. You would need something like the drug Flagyl for the yeast. That is why it is so important to seek proper medical attention. Im not downing you, I tend to self dx myself before heading to the doctor. Hope this helps.