Hello Kirsty Welcome to health care magic, I really appreciate your concern. Yes, sexually transmitted disease may cause lower abdominal pain. Looking at your description I would advise you to go for investigation to rule out possibility sexually transmitted diseases like blood for hemoglobin, CBC, VDRL test, serological test for herpes, test for candidiasis, urine culture and microscopy test or an ultrasound pelvis if need be. Another possibility of pain in stomach could be acid peptic disease or gastritis due to stomach hyperacidity. I would advise you to take antiacidity medicines like pantoprazole or ranitidine group of drugs with antacids for 2- 3 days, Have plenty of fluids which will help by flushing off the infection from the urogenital tract if it doesn t subside with it or you develop symptoms for STDs like burning sensation in urine, rashes in genital area than you need to go for above mentioned investigation to rule out possibility of STDs. Hope I could answer your question, please feel free to ask for follow up question I will happily answer you. Best wishes