No weight gain for 5.5 month old

My 5.5mo has a bit of a cough so I took him to the pediatrian today (6/12). While there, we got his weight and I was shocked that there was no weight gain since his 4month appointment on 4/30, not even an ounce. He is exactly 15 pounds. His regular pediatrian is out for the next two weeks, so the pediatrian he saw today said to make an appointment for him once his normal doctor returns.

Some things of note:

-Since 4/18, he has had really irregular stools. Most recently, he only pooped once in 8 days, before that it was 6 days. So loooong stretches.

-3/3 he was diagnosed with CMPA and reflux. He has been on Pepcid since, and I have cut out all diary and soy. We were doing one single night bottle prior to the diagnosis, but since changing to HA formula, he completely refused the bottle that bottle. So I have been EBF since 5/3.

-he rolls some but not constantly. He gets really frustrated during tummy time. So I don’t feel like the no weight gain is due to movement.

-he wakes up to feed in the middle of the night 0-1 times the past 3 weeks. Sometimes he will sleep through, sometimes he wakes and I feed him.

Since I have to wait 2 weeks for his doctor to come back, I am spiraling. Is this my supply? Is this normal? Should I start bringing in a dream feed? I would really love any insight or advice.