Hi, Usually vitamins may not be responsible for lower abdominal pain. Sometimes excessive thinking about the pregnancy can lead to symptoms that mimic pregnancy, which is called as spurious pregnancy. To find out the exact cause better, please consult your gynecologist once, get examined and undergo an ultrasound. This will help in finding the possibility of the pregnancy, in absence of pregnancy, it can help in finding the possible cause of pain abdomen. Regarding fertility, to increase the chances of pregnancy, both husband and wife should be evaluated to find out the possible problem, then treatment should be planned accordingly. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Sree Gouri S. R., OBGYN