I bet your problem pre-existed transplanting, they look very unhealthy and even pretty small for 3 1/2 week old seedlings. I generally let them get as big as they can in the size of cup I start them in then transplant, I had plants started from seeds reach a foot tall or more after a month then transplanted into larger cups, they have doubled in size over the past 30 days. I didn't give them any nutrients until after the first transplant.