What could cause a tooth infection not to show up on xray not even the panoramic ct. also ibe been prescribe an antibiotic for after extraction but since i been on so many antibiotic during the course of infection will this last one work?

You could have a gum infection, a tooth infection would have some evidence on an x-ray. The antibiotic for an extraction should be effective for your oral infection.

X/rays/CT scans do not show presence or absence of infection. They show the physical damage to the bone in the area from the pathogens. Sometimes that's not easily visualized. Infection soften diagnosed by symptoms and/or blood tests. Antibiotic coverage may be required post-extraction as the bacterial cells have already entered your blood stream. Follow instructions and you will be fine.