I have 4 non-GMO heirloom tomato plant. They are producing fruit however, all of the leaves are now very sparse and not growing near the top of plants. More stem than leaves and they are very tiny. I water every other day so I would like to know what could be wrong. I did find some of the lower leave yellow with black spots.
Are these plants in the ground or containers?
Tomatoes grown in containers may need daily water and even twice a day if the weather is warm.
You also need to make sure that the soil is well draining and that the roots are not in soggy soil.
Tomatoes do need full sunshine.
The yellowing leaves as well as spots could be watering issues, pests or more serious disease issues.
These links will help you pinpoint the issues.