Stupid O2 sensor

ok...i put a header and high flow cat on my 97 civic ex...my check engine light came on and i checked the scanner and it said my o2 was out or bad...when i put on the header and stuff i had to move the sensor...i bought the o2 extender from dc sports and bought a new o2 sensor...i reset the computer and i didnt even get out of the parking lot of the parts store and it came back on....help...