Tired Baby

FTM here...baby girl born 9/6
So our little girl is super tired whenever it comes to breastfeeding. We typically have to wake her up at the 3 hour mark to feed her. She latches on 1 side, feeds for about 5-8 mins (tho I usually have to rub her head often), burp her, switch to the other side and she feeds about 3-6 mins with me rubbing her head a lot again. She just gets so tired or something. Any advice? Thanks!!