Signs of being full/ supplementing questions

I'm a FTM and I'm breastfeeding I can't tell if she is getting full or even eating enough. She has a blood disorder that makes her really sleepy so now I'm having to start pumping and supplementing because she hasn't gained any weight in 2 weeks now almost 3 weeks. Of any of you ladies have had to supplement how did you guys do it. I feel so worthless that I can't even feed my baby properly. I need some advise!!