Skinny guinea pig

UPDATE : on jan 7th, my baby has passed. As he was dying a vet was kind enough to look into why he might’ve died for free and told me it was an issue with his organs, most likely a long going one so it wasn’t anything I did since I only had him about one month from when I adopted him from petco. I presume previous owners could not afford to take care of his issues or simply did not care. I know I did my best to give him a good remaining life and was spoiled to no end. ❤️ RIP

hey everyone, i recently adopted a guinea pig that was abandoned by their owner in a petco, he had slightly overgrown teeth and also extremely underweight which i didn't notice right away. over the past month I have been able to fix his teeth problem, simply giving him lots of chews and hay etc, but I have been struggling to help him gain weight, I give him lots of hay, lettuce, carrots, celery, parsley, and I've even recently tried oats. none seem to be working that fast from what I can tell, he seems very picky and cuz of his recent teeth problems, a slow eater. is there anything else I can try?? if not I was going to resort to critical care, I just got him like dec 1st but he seems past a year old.