pain during intercourse lower abdomen

okay...I have been having lower abdominal pain during intercourse for about six months off and on. I have been to my OB and had my exam he said that everything seemed fine however I did have a bacterial infection and put me on some meds. The pain did not go away entirely however it did ease up. Sometimes when I'm doing everyday activities I have very sharp stabbing pain in my abdomen and it continues for about three or 4 days until it eases enough that it is a faint ache but I continue to have pain during intercourse it feels like the first time over and over. I recently went to my family Dr. he ran some blood work, did an ex-ray and sent me for a ultrasound. However again I've been diagnosed with a bacterial infection and nothing else however I still have the pain. I'm not going to let it go because I know that it is not right for my body. I should not feel like this. I'm getting discouraged though. aNY THOUGHTS on what it could be. I need help I'm going to go beck for more test but I fell like I'm at a dead end. HELP! I have look up a lot of things on google and I know that there are some different things that it could be but if the ultrasound did not pick it up what is next?