Exclusive pumping

I've been breastfeeding for 3 months but my baby is now screaming everytime I try to nurse him so it looks like I'm going to have to switch to pumping. For those of you exclusively pumping how long have you done it for and did your supply decrease. I'm worried I won't be able to keep up and have to switch to formula. Also I'm open to tips on how to get him back on the breast. So far lactation consultants haven't helped much...