nyceclss

Can any1 help me PLEASE!!!! i have a 94 na manual n its a nightmare right about now. i went through 4 alternator in 1 1/2 weeks. i have an OPTIMA RED TOP for my car. This is the wierd part though, the car chargers during the day but at night when I will need headlight & heat since im in NY the voltage will start at 14.1 then continue to go down until I turn the heat off and/or the heat. I had a valve cover leak but I replaced that and change starter, alt, & batt.. CAN SUM PLEASE SHINE SUM LIGHT MY WAY?