Is this the soil you’re using? If not, could you kindly post a link to what you’re using?
If you’re using what I linked, there’s typically only a starter nutrient charge that allows plants to get about as big as yours before they need nutrients. It’s intended to be used with compost or other plant food/nutrients through the growing season.
Do you have a plant nursery or garden store around? Even the garden section of Walmart should have a semi-decent supply of plant food.
They’ll usually sell a basic 10-10-10 fertilizer that’ll get your plants into a better state. I’ve seen people have good results with simple stuff like that. Long term I’d look into the Jack’s 321 program (search for several good threads).