Ginny, it may be some nutrients deficiency.
"Yellowing of new leaves could point to iron or calcium, but iron chlorosis is characterized by uniform yellowing with small, green veins. For more details, see the infographic below and this guide by the Texas Agricultural Extension Service."
http://hortipm.tamu.edu/ipmguide/nutrient/diagnosi.html
Little Epsom Salt would not hurt (source of Magnesium).
Tomato-tone has Calcium and Nitrogen, I belive.
Can it be from overfeeding?
Sorry, not much help.