Hi, Welcome to HCM You are stressed out and tensed about getting pregnant and that is the cause of weird sensation that you are getting down your abdomen. Just relax, do not worry. 1. Developing UTI infection can cause tenderness of the lower abdomen after sex. Get urine test ( culture and routine ) done to rule out E.coli infection. If test is positive, norfloxacin can help, take medicines after clinical examination by an expert. 2. The other cause of pain lower abdomen can be due to irritable bowel disease, gastritis, cysts, developing fibroid, any pelvic inflammatory disease or acute infection. Get assesses by a gynae. 3. You should avoid unprotected sex. Use barrier methods and pills to avoid unwanted pregnancy. 4. If you do not get your menstruation in time get a pregnancy test done and get treated before its too late. 5. Take care of your hygiene, drink plenty of water. Take care.