Baby having trouble going from bottle to breast

I gave my 7 week old 4 bottles for the first time this weekend (hes only had 6 bottles since birth). Now when he is at breast he seems so upset (I'm assuming because its slower). He has nursed for 3 hours straight today (cries immediately if I take him off). Starting to make me feel like he cant get full and my milk supply has dwindled? Or is this normal? Any tips are appreciated! Also, should I let him nurse for 3 hours? I've changed him, given paci, rocked, tummy time, nothing will make him happy!