I have a male guinea pig I got from petsmart, I do NOT support buying over adopting, however he was clearly sick and very badly beaten by the other guinea pigs. When we got him he seemed to get a bit better, only minor symptoms of his URI. So we waited a bit before getting him into a vet for some antibiotics. The vet said he was very young and far too young to be sold or taken from his mom yet,he was said to be no more then a few weeks or so. She gave us Doxycycline for him and we gave him .25 ml of it. After about 3 days on it he drastically got worse, his URI was in full swing and he is now coughing and has a ton of gunk around his nose and eyes that I clean every day twice. He eats and drinks normally and is eating hay and pellets along with veggies and rarely watermelon for glucose. However today is the worst. I started giving him a little bit of kitten milk formula because even though he's eating a bunch he's super boney minus his belly which is plump. He has a heating pad, food, water and I gave him his morning dose of Doxy. However he is still on the verge of death. I think I should stop the doxy and maybe it'll help, because while it could be a coincidence that his symptoms got worse after taking it, I still don't think it's wise to give him any more. I syringe fed him water with a drop of vitamin C in it to maybe get him moving around again but he is strictly eating and sleeping with no more bouts of energy anymore. What do I do? I have no money because I spent 997 dollars getting my cat taken care of and my other guinea pig a C-section which cost 230 dollars. I don't think there's anything left to do, but because he's still eating and drinking I want to have hope, but he is so unresponsive and every time I pick him up he doesn't struggle and goes limp unlike before when he would kick me out scratch my arm after putting him in his house again or picking him up. Any advice on this situation? Would taking him to the vet again be futile now or should I give it a shot? Any advice helps.