Hi deb, try from small seedlings rather than seeds if you haven't.
Sounds like the soil in the pots doesn't have enough nutrients even though you feed.
Or if you have fed too much, the new young roots will burn and the plants won't develop.
I would empty the pots out and mix current soil with some new and put a few dynamic lifter pellets on the top to let the rain or watering slowly dissolve them down into the soil but not near the young plants. This will also mean the roots will sniff out the nutrients and reach for the sides of the pot where the pellets have seeped in.
I do tomatoes in pots as well, but there I use tiny tomatoes or cherry tomatoes.
Always get soooo many that I need to watch out for acid reflux. Too easy to eat. 
