Baby not latching

So I had my son on the 28th and I'm so frustrated! He was latching perfect and we were doing good but since yesterday he isn't wanting to latch and will get frustrated and start crying and when he does he'll only stay on like a minute and pull off and start crying again. I've had to start pumping and I'm only pumping like an ounce and a half from both breast so I don't think he's getting enough and it's making him upset. I don't know what to do because I didn't have this issue with my other 2 kids.. Any advice?