1 month old not gaining weight and very sleepy!

I'm looking for some feedback!! My 1 month old daughter was exclusively breast feeding for the first couple of weeks. She was 6lb 14oz at birth, and went as low as 6lb 3oz before she started to gain. At her 1.5 week weight check she was 6lb 10oz so we thought we were in the right direction. We then went to a new pediatrician around 2.5 weeks and her weight was only 6lb 8oz. They had me start doing supplemental nursing system every other feeding to test her ability to gain weight and after 3 days she was up to 7lb so we were happy. Since then, she hasn't gained any more weight in over a week. Was still at 7lb at her 4 week check even with continuing to supplement.

We decided after this to just bottle feed with formula and give her my pumped breast milk for some feedings so we know exactly what she is getting. I have noticed since she is getting more formula and frequent feedings that she is extra sleepy and very hard to wake up for feedings. During the day she might cry and give us cues that she is hungry but not always. In particular at night, she is very difficult to wake (usually takes me about a half hour to do so). On a side note, she has been sleeping through the night since she was only a few days old, with us always having to wake her for her middle of the night feedings. I initially thought this was great, but now I'm wondering if it is an indicator of something else going on.

So basically, I am concerned that the combination of her not gaining weight, being excessively sleepy, and having to wake her up for feedings could all be due to a bigger concern. We have another appt tomorrow to check if she is gaining. In the meantime, I am looking for some feedback as to other mom's experiences or any ideas on what could be going on PLEASE....and thank you in advance for reading ☺️👶🏼