Duncan is going to stop the Baytril soon, and is also on Metacam and Emeprid. I'm scared I haven't spaced them out properly, and also that he isn't eating or pooping enough, he munched some hay but is now pretty sleepy. I'm so nervous, what if he dies because I'm a bad owner?
He's a good weight, and when he wakes up I'll give him floor time to keep an eye on his poo. I just feel so guilty, and scared. Today he's had Baytril and Emeprid, a little while apart. He still needs Metacam, and another dose of Baytril and Emeprid. I just feel like a bad owner
Please take a deep breath and calm down! There is nothing wrong with Duncan and if you are anything, then you are an owner that is caring a bit too much rather than too little.
If he is holding his weight, then there is nothing wrong with him. Please remember that the poo output is not steady all the time and that it is always lagging 1-2 days behind. If the poos are still a good size and normal looking, then as a rule of thumb, your piggy on meds is ticking over nicely.
A guinea pig that is not eating enough, has noticeably smaller and thinner poos; one whose digestion is
little bit out of order from the baytril may have softer poos or tear shaped poos, but even that is nothing to really worry about and nothing that a bit of topping up syringe feed can't help with.
As long as a piggy is still accepting some food and water, it means that its digestion is still working and it is still able to process food, even if it is less than normal during an illness. It also means that your piggy is NOT about to die.

See a vet if shapeless cow pads don't firm up within a day of being off fresh veg.
Total loss of appetite/major weight loss (over 50g in 24 hours) and refusal of syringe feel combined with flatness and apathy when you need to see a vet promptly. You will see very small/funny, very few and often mucus covered poos if a piggy's digestion is runny totally on empty (including dehydration) or outright fluid diarrhea if things are really not right.
I hope that helps you as a rule by thumb guideline.
Baytril (like most antibiotics) is an appetite dampener, but once Duncan is off it, he should get his normal appetite back within a day or two.