Fussy nursing

My baby is 12 weeks old now. I went back to work at 8. He has been taking a bottle and nursing since 4 weeks without any nipple confusion. The last two days he has started getting extremely fussy when I try to breastfeed. Sometimes it's in the middle of it. Sometimes it's right when I put my nipple to his lips. I thought it was because maybe I have a forceful letdown but I've had an oversupply since probably 3 weeks. Never been a problem before. Plus he gets fussy before letdown at times. He has absolutely no problem taking a bottle. I'm scared he doesn't want to nurse anymore. He did such an amazing job until now. I don't know what to do... I feel like a failure.