Hello Ma'am, I'm sorry to read about your troubles!
Episodes of fever, as long as they are temporary, do not necessarily indicate a problem. At the age of 3, it is often viral and temporary. That being said, if the fever persists for 72 hours, i.e. a temperature that exceeds 38 degrees Celsius, it should be evaluated by a doctor.
This brings us to the present episode. I invite you to contact your pharmacist so that he/she can tell you the maximum dose of Tylenol that you can administer according to your child's weight (I can also do this if you provide me with your child's weight and the concentration of the product you have).
Decreased appetite is normal with illness, but your child should at least eat/drink during the day. I encourage you to give your child fluids often, even if it means giving smaller amounts more often. If this is not the case, or if his general condition seems to be greatly affected, you will have to consult more quickly.
I hope I've been helpful, and I'm available if you have any further questions!
Tom Samaha, pharmacist