Yes, My Companion Has Enlarged Prostate Diagnosed 08/15 , He

yes, my companion has enlarged prostate diagnosed 08/15 , he was having issues with urinating also erection ability , after take Tomillson medication he stated having issue again, Dr. stated he has prostate infection and prescribe him antibiotic doxiclycline . the antibiotic he seems to think makes him sick ad he will not take it nr go back to Dr., what are issues that can happen if not treated properly?