Not making enough milk?

FTM My lo 6 weeks sometimes screams when trying to breastfeed.. like full red face, top of lungs, deep screams. I don't know how to help him. I am not sure if it's because he isn't getting enough milk or what's going on. How can I help him? How can I increase my milk supply? What would impact my supply to make it less than needed? My lo feedings are not on any sort of schedule. I can feed him for 20 mins and he will want to eat again in less than an hour. I've tried to pump after feedings, but nothing comes out and I worry about taking milk when I don't know when he will want to feed again. Also, lately he has been wanting to use my breasts as a pacifier, sucking on them for a long while even after he has stopped getting milk. If I take it away, he will search for it and get upset if I don't let him go back to sucking on my nipple. Please help!