COMPANY AND PERSONAL DISTRACTIONS CONTRIBUTED B737 FLC IN CONDUCTING A WRONG RWY APCH.

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I WAS THE PF ZZZ-DFW. THIS WAS THE FIRST LEG OF THE FIRST TRIP PAIRING OF THE MONTH. I HAD NEVER FLOWN WITH THIS FO BEFORE. FOR MY FO; THIS WAS THE FIRST FLT AS AN FO AFTER BEING DOWNGRADED FROM B737 CAPT DUE TO FURLOUGHS/REASSIGNMENTS AT OUR AIRLINE. HE HAD PREVIOUSLY STATED THAT HE WAS NERVOUS ABOUT FLYING AS FO ON B737; HE HAD NEVER DONE SO BEFORE (HE HAD PREVIOUSLY UPGRADED FROM MD80 FO TO B737 CAPT ABOUT 2 YRS EARLIER). FOR BOTH OF US; IT WAS OUR FIRST FLT AFTER BEING XFERRED TO ZZZ AS A CREW BASE. BOTH HAD FLOWN INTO/OUT OF ZZZ AND DFW PREVIOUSLY. WE WERE BEING GIVEN RADAR VECTORS FOR VISUAL APCH TO RWY 18R AND RPTED ARPT IN SIGHT ON BASE LEG; BUT SOMEWHAT HIGH. WE WERE CLRED FOR VISUAL APCH RWY 18R AND TO CALL TWR. COPLT LOOKED INTO COCKPIT TO CHANGE FREQ. I LOOKED INTO COCKPIT TO CHK ALT; SPD; DSCNT RATE; ETC. WHEN I LOOKED OUTSIDE; I CONCENTRATED AND TURNED TO A HEADING TO LINE UP WITH RWY 17R. WE HAD TUNED/IDENTED ILS RWY 18R; BUT FLEW THROUGH IT BY MISTAKE WHILE LOOKING OUTSIDE AT INCORRECT RWY. AFTER GOING ON A SSE HEADING ABOUT HALFWAY BTWN RWYS; TWR STATED WE APPEARED TO BE APCHING THE WRONG RWY AND IF WE HAD ANOTHER ACFT IN SIGHT FOR LNDG ON RWY 17C. I REALIZED MY MISTAKE; HAD OTHER ACFT IN SIGHT SAFELY AND TURNED TO LAND SAFELY ON THE CORRECT RWY. I HAD A POOR NIGHT'S SLEEP PREVIOUS TO OUR XA50 CHK-IN AFTER COMMUTING IN TO WORK THE PREVIOUS EVENING. I SHOULD HAVE REALIZED SO MANY FACTORS COULD HAVE COMBINED TO CREATE A PROB AND CONCENTRATED BETTER. I WAS POSSIBLY TRYING TO DO TOO MUCH; TRYING TO HELP FO IN HIS NEW POS. HE WAS PROBABLY SOMEWHAT 'BEHIND' ACFT ON THIS SHORT FLT DUE TO INEXPERIENCE AS FO; AS I WAS NOT TOLD WE WERE FLYING THROUGH LOC NOR APCHING INCORRECT RWY.