Cherry tomato plant has scattered yellowing leaves. What is wrong with it?

Cherry tomato plant has had all its lower leaves yellowing and dying. There are yellowing leaves all along one branch and scattered yellow leaves throughout. The plant has not grown in awhile though it is an indeterminate dwarf cherry tomato. It was planted as a seedling 4 months ago. Originally thought it was nitrogen deficiency and gave it liquid fish fertilizer but the problem has persisted. I have been feeding it organic Dr earth tomato fertilizer (4-6-3). Is it possible I have overfertilized it or that it has a disease? I also had 5-6 caterpillars on it 2-3 weeks ago that ate some of the green tomatoes and I picked them all off. Could that have caused it?