Giving it too much water OR your not giving it time, I sorta know cause my dad once grew his own tomato plant, not sure if he does at this point. Give it at least a week or 2, don't rush it or you won't like the results or you won't get anything.
It is probably because they are getting too much water or too little water or too much sun or too little sun. Try to feed them less or more. Possibly they are not tomato plants at all..