I would buy a double electric pump and pump both breasts the use of the pump may fix the inversion. On a reasonable suction setting it won't hurt and it may relactate. You could also try reglan or domperidone to increase your supply but an efficient pump will help more.
Wake up and pump between 2-5am it's when your body produces the most and you may be pleased with your output at that time.
Don't give up you are doing amazing every ounce adds up.
Mommy to Patrick 05/19/05, Parker 11/20/09 and Paxton Arrived 2/14/13, Penelope 5/29/14