I sleep trained my baby and my milk production decreased. I've started extra pumping and nursing but it hasn't come back in a month. What to do?

Keep it up! Keep working at it. Breastfeeding is a supply & demand phenomena, and the more demand you create, either thru nursing or pumping, the more supply you'll generate. Frequent nursing also helps; you may want to consider trying to pump or nurse right before you go to bed in addition to the other times you are already. So that's what they're for by j. Todaro is best book about breastfeeding.
Nursing, no pumping. If your child is being fed by the bottle, which is so much easier and quicker, he/she is less likely sucking effectively at the nipples, thus reducing stimulation and consequently reducing milk production. Pumping does not really work...Women around the world who have no pumps, never really seem to run out of milk..Breastfeeding for 2 yrs..Eventhough they don't even get enough food..Amazing.