Fussy at the breast

My son is almost 3 months old and for the past 4-5 days he nurses for about 10 min and then unlatches and latches back on, the repeats 2-3 times and then starts screaming... Same thing happens when I switch breasts... I already pump 2-3 times and give him the breast milk at the next feeding but I cannot pump more often than this... I presume he may be getting unhappy when the flow slows down... I don't want to give formula because this will impact my milk supply... Any other baby being fussy? Any ideas?