Breastfeeding struggles

La
I am struggling with breastfeeding. Not sure why as this is my second child but this time around its not going as smoothly. 
My little one just turned 3 weeks; we are struggling with latching properly and now he is nursing non-stop. So much so that I cannot keep up and I have had to start supplementing. I also have started supplementing because he was not gaining weight like his pediatrician wanted him to be.   I am so frustrated. I started taking the fenugreek and blessed thistle which was recommended by the lactation consultant but I don't feel like my supply is improving. Trying to pump on top of breastfeed but I just don't understand when I am supposed to have time to pump between feeding him and trying to keep my own calories up. I am exhausted. Anyone have any helpful tips?