It is possible that your mulch is tying up nitrogen as it tries to decompose. Add some source of nitrogen that won't burn the plant (
coffee grounds,
urine, rabbit manure...) and see if that helps out. From what I hear, that is the biggest mistake "back to eden" newbies generally make. As to the sun issue ~ I have peppers growing like weeds in the understory of an oak tree here in central texas. They get direct morning sun for about 4 hours, but then the tree and the house partially shade or completely block the sun for the rest of the day. EVERYONE who saw me put them in told me it wouldn't work. Suckers.
I'm glad I ignored them. Good luck finding your solution!