If you have never had sex before then most likely you have a UTI . You have the classic symptoms such as burning when urinating. Sometimes that can be worse than others.There may be pain in your tummy or lower abdomen. You may have pain in your lower back as well. There is sometimes a feeling of being just washed out and fatigued. You are tired all of the time.You alo may have the urge to go but you can't.
If there is blood in your urine or if it looks milky and cloudy, that's a symptom. Another cause can be diabetes as well. This can cause the same type of issues. This is how my father found out he was diabetic.
Vitamins shouldn't do this to you. Have you been taking in lots of sodas or not enough water?
Keep in mind UTI's are usually caused by bacteria so thee symptoms can occur. It is highly unlikey that you have an STI , without sex, unless you had genital contact with another person.
Call your doctor and let them know your symptoms. He or she will have you come in to do a simple check and prescribe anitbiotics. You should feel better once you begin taking them.
I hope that helps you out