Feeling very discouraged with breasfeeding... kind of long?

I've been having troubles since the beginning when my little on lost over the recommended amount of birth weight. I've had to supplement - and now that he's 4 weeks old I've only been supplementing him with 2 oz once a day instead of 3 times a day. He was slightly above his birth weight 2 weeks ago. My concern is that I just watched a video of what a good feed looks like and I can honestly say that he only sucks-pauses-swallows steadily for 2 minutes before he nibbles. So now I'm horribly worried that he'll have lost weight at his doctors appointment tomorrow. I'm so anxious and sad and disappointed with my since I've been told several times that his latch is good :( Any advice?