Sleepy Baby while Breastfeeding - Help!

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I’m a FTM with a 3-week old and we are just now getting the hang of nursing in the past couple of days (long story as to why, but was medically necessary to supplement & it’s not been easy coming back from that). However, he always falls asleep while I’m nursing and sessions can take close to an hour! It’s exhausting. I’ve tried tickling him, blowing gently on his face, changing positions, burping him, and giggling my boob in his mouth. What can I do to keep him awake enough to finish eating?

Note: I do use a shield because I have shallow nipples and he’s not the most observant baby, even when I sandwich my boob and put it in his mouth.