Once it happened to me that my seedlings were about 4 - 5 weeks with the size of a 1 week old plant, I wanted to die, I had high temperatures and low humidity in the indoor.
I had no way to lower the temperature, but I managed to increase the humidity, then they exploded in an incredible way.
Give it love and time, if you can lower the temperature, but try to increase the humidity if you can!
Good luck