Problems flowering

Hi everyone i really need a bit of help my plants were doing great till i started to flower them i went from 18/6 to 12/12 iam using a 125w cfl grow lamp in a small cupboard painted white inside iam only growing two white widow plants ive used a good soil mix and only used plant feed a few times. the plants had started to wilt once i changed the bulb and then the leaves started to turn yellow with brown spots. please can you help any advice would be very grateful