Vomiting, really sick Axolotl.

I’ve had my Axie SharkBait (ho ha ha) for nearly a year now, and he’s been doing very well, and growing nicely (he’s just a juvie). But last week around thanksgiving I noticed he was floating...oddly. It wasn’t his normal “I took in air and am up here now mom” kind of float. He was nearly on his side, and his left back leg was sticking straight up out of the water. I blew on him and pet him a little and he made a valiant effort to swim back down to the bottom of his tank, but his butt was still sticking in the air and it made him float back up. After a couple of tries, I put him in his container that I use for grudging and cleaning, and he started to throw up food...and tiny rocks. Note; yes, some parts of his sand at that time had tiny bits of pebble, and I knew this would possibly be an issue and I was a bad first time mom and didn’t take the necessary precautions. I put him back in the tank and he floated down fine and looked pretty healthy and great! A few hours passed and he was floating again, but no vomit. The next day I made the decision to fridge him, which terrified me because I’d never done it. In this time I did a 100% change of his water, let it sit for a little over 48 hours and made sure to buy him new, safer sand. After the fridging process I put him back in his tank after getting him adjusted to the water again and he had never looked healthier! That was until yesterday...when he started floating again. I don’t know what’s wrong with him! I know he doesn’t have a blockage because he has been pooping. But today he’s been violently vomiting his food back up and I don’t know what to do! I’m leaving this weekend and I’m scared something is going to happen to him. I feed him these salmon pellets that his breeder sold to me. I give him one a day, maybe that’s too much? That’s what the guy told me to give him but maybe he’s too big now or something? Please help!

That's not to good... :/ do you know the parameters of the water are? What temperature is the water normally? Sometimes they can get sick from the water being to cold for them - do you know what the temperature was while he was in the fridge? Is the axie exposed to bright lights for long amounts of time? I read somewhere that that can upset the little guys. It sounds like he could be a little stressed.
I'm gonna try help you out the best that I can..
I love his name and I hope he's gonna be alright,
- Chloe

His water temp is normally around 16-20 degrees Celsius, and the highest it’s ever been is 22 with the lowest being 16. I don’t know the parameters at this moment but I’m going to go get his water tested. I’ve done this before and it’s been perfect (he had fungus at some point but t went away fairly quickly). Right now he’s been back in his tank for two days. I had him in the fridge for about five days and he looked a lot better. Each time he’s fridged he looks better and is able to stay down on the bottom of the tank, but then he starts floating again. This time he’s on his side floating and is a lot more lethargic and unresponsive. He isn’t exposed to any lifts regularly, just the ones in the fridge mostly. But I covered his little container with a towel so they wouldn’t bother him as much. Unless I turn the lights on in the room where he’s located, which I don’t very often, he doesn’t have more than the lights from behind the curtains on him. Thank you for replying, I woke up this morning and the little dude just looks so miserable

maybe he is constipated?? if his butt is floating it could mean constipation