C., Good Morning. Don't worry he will go back to where he was before. We JUST went through this with our 3 y/o Gr. son. He ran a very high temp for 5 days spiking at 104 several times, before we Finally got him in to dr. grrrrrrrrrrrrrrrrrrr Wanted to slap a knot on the back of Dr.'s forehead too. lol
We did the pull up thing to, cause he just laid around doing nothing but sleep.
He will be ok just give him time to re-adjust. Keep taking him to potty, even when he says No he doesn't need to go.
We are just about back to where we were also. He pooped twice in potty so far. YEAH!!!
Side note, Not sure what your Dr said about a fever, But I was livid with ours, and it certainly makes sense the way he explained it. Oh But I was ticked!! A Temp ( numbers ) isn't important ( ONLY TO WORRYING over reacting GRANDPARENTS ), it's only important that they have one, it means their immune system is doing it's job. He said it was like a Very Sick person with Aids. They are some of the sickest people ever and they have No fever cause their immune systems are shot. Also he said Using the word lathargic is Thrown around by Parents Way to much.
Hang in there C., he will get back to where he was, just going to take some patiences on all parts.
God Bless
K. Nana to 5