This is not an std if you haven't had sex to cause it. You don't mention any unsafe sex but just the antibiotic use. Antibiotics are notorious for causing yeast infections and yes, a little irritation can result in blood in the yeast discharge. If it itches and has the curd like discharge, it's yeast which makes sense. You can talk to your doctor about what you want to do to treat it. either over the counter or a pill they can prescribe. If you are having unprotected sex, or even just sexually active though, you should have a routine STD check (regardless of yeast infection). Good luck