Low milk supply at night?

I have a four week old, and for the last few days I’ve noticed that my supply seems lower at night. Throughout the day he has no issues eating and swallowing, but in the evening he is getting so frustrated! He pulls off of the breast, cries, slaps his hands around. I see that milk is coming out of my breast, but not nearly as fast as during the day. I end up giving him an ounce or two of pulled milk in a bottle at this time because he is so upset! I don’t want to have to continue this, however. I would much rather him be strictly breastfed when I’m home. How can I help with his frustration? Is there something I can do to increase my supply at this time of day? By the middle of the night, my supply is back up again and he eats very well.