DD was slightly jaundiced at birth as well. The sleepiness is very normal as part of that. Took a week or two of feeding and sunlight to clear up.
She was so lethargic at feeds, when she bothered to wake up that is. I had to strip her all the way down to her nappy. Then change her nappy mid-feed, all the while tickling/rubbing her to mildly irritate her and keep her awake.
I also laid her out in her Moses basket, wearing only a nappy, next to a window for a few minutes every day. Sunlight really helps break down the bilirubin. Naturally you don't want direct sunlight, or to leave them for very long, buy I felt it did help
Eventually we did a feeding regime. I'd set an alarm for every 3 hours, day and night, and I'd do whatever it took to wake her up enough to feed. I did this for two days, but by the end of it, she was more awake and feeding so much better. It was absolutely brutal doing it, but it was necessary.
GL @erised24. Definitely call your midwife/HV for some more advice.