Breastfeeding

My little one is one month and I'm breastfeeding him though I have to use a nipple shield. He struggled the first week then wks 2-3 he was latching on. Now he cries and even though it's in his mouth he struggles to latch on. I've tried getting him before it's time. I also have been bottle feeding him once a day as well so that my husband can feed him while I rest. What am I doing wrong? This is upsetting and stressful seeing him like that. Any advice or suggestions will be greatly appreciated. TIA