What Causes Severe Pain During Intercourse?

I have been in a relationship with a man for about 9 months. For the first 6 months everything was great, but in the last three months during intercourse I am experiencing a lot of pain - to the point where I do not want to have intercourse anymore. I have been STD tested and have been treated for a kidney infection. I am wondering if I could possibly be allergic to Astroglide as I can't pin point what else could be wrong. My gyno had no ideas and blamed it on stress, but that doesnt make sense.