Does my milk not have enough fat or nutrients ?

So my LO is 3 weeks old today, for the past 2 weeks she has been eating a lot, and when I say a lot I mean between 4-5.5oz per feeding. Sometimes even asks for more half an hour later, so she drinks another 2oz or less. We were at the docs last Tuesday and she had gained 1 lb in one week and the doc was amazed and said she's perfect and gaining weight perfectly. Now I'm starting to notice she's sleeping 1-2 hours less and asking to be fed more frequently. So I'm just not sure if maybe my milk doesn't have enough nutrients or isn't fatty enough to keep her satisfied for longer like it used to. My diet really hasn't changed or anything so I'm really not sure what's going on. I'm thinking of just taking her to the docs Tom and maybe checking her weight.