Dear Betty, 
I apologize for the lateness in responding to your email. 

The short answer is that you need to do a soil test first to determine what nutrients are available in your soil. UMass soil tests can be accessed at: https://ag.umass.edu/services/soil-plant-nutrient-testing-laboratory/ordering-information-forms
Follow the directions for collecting a soil sample and fill out ans submit this form: Routine Soil Analysis - Order Form for Home Grounds and Gardening
Here is more information on fertilizing tomatoes from UofMaryland https://extension.umd.edu/resource/growing-tomatoes-home-garden/

• Fertilizer needs: High requirement for nutrients, either from soil organic matter or fertilizers. Use starter fertilizer for transplants. Side-dress after first fruits appear. Additional fertilizer may be needed depending on plant growth, fruit load, and soil fertility. Do not add Epsom salts (magnesium sulfate) to the soil unless soil testing shows a magnesium deficiency. Refer to Fertilizing Vegetables for details.

And more information from the Fertilizing Vegetables link after you have the results of your soil test:

Vegetable fertilizer tips

• Refer to the label directions of the fertilizer you select for the amount to use.
• Fertilize spring seedlings and transplants with a soluble fertilizer mixed with water then switch to a granular vegetable fertilizer as the plants grow.
• Mix dry fertilizers into the top 2-4 inches of soil. Water-in fertilizers after application if rainfall is not expected.
• Nutrient availability is reduced by competing weeds, leaching and run-off, and cool spring soil that limits nutrient release from organic matter.
• Fertilize the actual planting area where roots will be growing, not walkways.
• Slow growth, stunting, pale leaves, and low yields may indicate a need to fertilize. But these symptoms can be caused by other factors, such as crowding, low sunlight, compacted soil, and root-knot nematodes.
• Sidedress established plants (apply fertilizer next to plants) when needed. Pull mulch away before sidedressing and replace it afterward.
• Use nitrogen-only fertilizers (organic fertilizers) rather than complete fertilizers (contain N, P, and K) if a soil test report indicates high levels of P (phosphorus) and K (potassium).
• One cup (8 ounces) of a dry organic fertilizer like cottonseed meal weighs approximately 0.33 lb. (5 ounces).
• One cup (8 ounces) of a synthetic granular fertilizer like 10-10-10 weighs approximately 0.50 lb. (8 ounces).
• Boron is an important micronutrient that is sometimes deficient in sandy soils causing disorders in some vegetable crops. If a soil test report shows a low Boron level dissolve 1 tablespoon of Borax in 1 gallon of water and apply the solution evenly from a sprinkling can over 100 sq. ft.
• Overfertilizing vegetable plants (especially nitrogen) can produce lush, green plants but little fruit.
• Both chemical and organic fertilizers can be overapplied and burn plants or stimulate leaf growth at the expense of fruit."

https://extension.umd.edu/resource/fertilizing-vegetables/