What is the environment like? Indoor or outdoor? Temps? If any fertlizer what did you use and how often? Have there been any treatments for any bugs?

Temps have been not to high 40 to high 60 to 70 I bring them in at nights fertilizers is jobes organic tomato fertilizer and I have used no treatment for bugs

I have had these plants 3 weeks only fertilizer once

40's is too cold for peppers to be outside they like minimum 60 for the root zone, many including myself have left peppers out in the 50's but that's fully grown peppers in the transition from summer to fall. Seedlings and younger plants such as you have I would stay away from those temps. My advice would be to keep them warm and watch the new leaves for health. If they are healthy then it's from the cold.

Ok

Let up on the fertilizer, too.