Sleep doctor's clinic says CPAP can't be the cause of weight gain

I started CPAP therapy 5 months ago and have gained 20 pounds since then. I didn't have any major medication or diet changes - in fact, I've been actively trying to do better health wise. I cut caffine completely and exercise 5 times a week. Which is why I feel like I'm being gaslit about my weight gain. I have been feeling very negative about my weight and body image, so I reached out to the sleep doctor's office to get some insight. I was told that CPAP can't be the cause of my weight gain and I should reach out to my primary doctor.

I searched "weight" on this subreddit and have found many posts about cpap weight gain- so how could that be such a common experience but be disregarded by my doctor???