The ideal approach would be to contact the pharmacist who provided you with the antibiotic, as they have all the necessary information to better assist you. Pain in the lower abdomen, around the bladder area, can be a common symptom of a urinary infection. It may take up to 72 hours after starting the antibiotic for the pain to improve. It's important to know when you started the antibiotic and how long it was prescribed for. Additionally, knowing at which week of your pregnancy you are currently in is important for understanding your situation.